Is illegal downloading a sin?

While I do not believe it would be sinful as stealing, it is sinful as a result of two other different reasons. First, biblically, it is clear that, in so far as it is not in conflict with scripture, we should follow the laws of the government over us. As illegal downloading is illegal, it makes it a violation of those laws that is not in conflict with the scriptures and thus sinful.

Additionally, James 4:17 likely makes this sinful as it says "Anyone, then, who knows the good he ought to do and doesn't do it, sins." When you consider the loss to the owner of the work by using it without paying for what you use, even if it doesn't directly cost them anything, I think it is a hard argument to be able to say with a clear conscience that it is good to take without compensation when compensation has been asked for in exchange for use.

Simply, Yes.

From dictionary.com:

steal [steel] verb, stole, sto·len, steal·ing, noun verb (used with object)

1.to take (the property of another or others) without permission or right, especially secretly or by force: A pickpocket stole his watch.

2.to appropriate (ideas, credit, words, etc.) without right or acknowledgment.

3.to take, get, or win insidiously, surreptitiously, subtly, or by chance: He stole my girlfriend.

4.to move, bring, convey, or put secretly or quietly; smuggle (usually followed by away, from, in, into, etc.): They stole the bicycle into the bedroom to surprise the child.

From the National Crime Prevention Council

Stealing intellectual property is cheap and easy. All a thief has to do is copy someone else’s ideas or product. The other person or company—the victim—has done all the work, but thieves can reap huge profits. Intellectual property theft can cost people their jobs, damage the reputation of the original maker of the counterfeited product, cause sickness and bodily harm, deprive governments of desperately needed tax revenue, and even result in the spread of organized crime and gangs—which in turn can damage more lives and destroy neighborhoods. It isn’t a victimless crime

The Catechism of the Catholic Church defines theft as:

2408 The seventh commandment forbids theft, that is, usurping another’s property against the reasonable will of the owner. There is no theft if consent can be presumed or if refusal is contrary to reason and the universal destination of goods. This is the case in obvious and urgent necessity when the only way to provide for immediate, essential needs (food, shelter, clothing... ) is to put at one’s disposal and use the property of others.191

It is a sin because it is stealing. I think there is even a splash screen on most movies that says illegal downloading is stealing. There are many lawsuits that have been going on right now about when it is considered theft and when it is not.

Having said that, it is still worth considering the original question: is illegal downloading a sin? ... it is ... undeniably a dishonest act, which is sinful. It is also illegal, which calls to mind Paul's admonition in Romans 13: 1 that Christians are required to obey the law.

So yes, it is a sin of dishonesty....

To give any useful answer, it is necessary first to understand what stealing is, and why it is considered a sin.

Theft (stealing) is taking possession of something away from its legitimate owner without justification. (Taking something is justified, for example, if it is given as a gift or purchased/traded in a fair deal.) It is considered sinful because it causes harm to another person, by depriving them of something of value. Stealing another person's money causes them to not have that money anymore, for example. This sounds obvious, but it's important to keep in mind.

When a copy of something is made, without damaging the original in any way, no harm has been done and nothing of value has been removed from the owner's possession, so in that sense it cannot be considered stealing.

We can see that the assertion that "in the creator's purse there will be less money" is clearly false. What is true is that in the creator's purse there will not be more money, but that's not the same thing unless one assumes that every copy made equates directly to one lost sale. But this contradicts the stated premise that many people use illegal copies because they cannot afford to buy a legitimate copy. (If they did not have their illegal copy, they still would not have bought it, because they do not have the money.)

In fact, studies consistently show that one illegal copy is equivalent to much, much less than one lost sale. Depending on various factors, results tend to vary from one copy being 2-3% of one lost sale, to around ten thousand copies equating to one lost sale. And being unable to afford the purchase (or simply not wanting to pay for it) is only one of many factors that motivate illicit copying, and not even the largest factor in many cases.

Equating illicit copying with theft is a highly cynical and highly deplorable act that is employed to alter the public discourse. (If C. S. Lewis were alive and writing The Screwtape Letters today, he would certainly have mentioned it as one of the more effective fruits of the demons' language manipulation program!) Ironically, this manipulation of our language has been used to justify several legal and policy changes that greatly facilitate actual theft and other crimes against real property.

For example, there have been many many cases where bogus copyright claims have been used on YouTube to deprive video creators of their rights and either place unwanted advertis*m*nts on them or redirect the income from existing advertis*m*nts to the persons making the false claims. This represents a direct diversion of income from a person who created something to a person who had nothing to do with it, simply by the thief taking advantage of systems put in place to combat "theft" that is not theft at all.

Also, consider so-called "digital rights management" on software and other digital media, which was legitimized by various copyright acts around the world. Its stated purpose is to prevent "theft," but its actual effect is to rob a computer owner of their natural right to control their own property. (While having zero actual, measurable effect on illicit copying.) In any other context, installing software onto someone else's computer whose only purpose is to take away their control over their system would be considered an act of hacking, and yet the misappropriation of the word "stealing" allows deplorable acts taken to combat it to appear legitimate and justifiable.

Having said that, it is still worth considering the original question: is illegal downloading a sin? Even though there is no reasonable justification for equating it with stealing, it is still undeniably a dishonest act, which is sinful. It is also illegal, which calls to mind Paul's admonition in Romans 13: 1 that Christians are required to obey the law.

So yes, it is a sin of dishonesty, but I would argue that calling it "stealing" when it clearly is not is a sin of dishonesty as well. And if we measure the severity of a sin by the amount of harm that it does, than the misappropriation of the word "stealing" is by far the worse sin of the two.

For the purpose of this answer, I will assume that intellectual property theft means making or using copies of someone's designs or data without consent or against their terms of use.

Now, the Catholic Church holds several basic beliefs that suggest intellectual property theft is sinful. The mode of sin can be considered theft, and in some cases, false witness.

First, and however insignificant the effect, intellectual property theft requires the intellectual property creator increase the price of their product to yield the intended income from producing that product. That is, stealing intellectual property drives up the price of that intellectual property for other consumers and/or puts the business at risk. According to the Church, this a form of theft, both from the producer of the IP and the intended consumers.

Even without a measurable hike in price or loss for the business, it breaches the social contract, wherein the intended consumers are placed at an economic disadvantage. E.g., if you, doing your civic duty, pay $1000+ for some useless Adobe suite, only to find that I have a pirated copy; you're going to feel cheated. (So would adobe, if they ever found out.)

Even if it does not contradict the provisions of civil law, any form of unjustly taking and keeping the property of others is against the seventh commandment: thus, deliberate retention of goods lent or of objects lost; business fraud; paying unjust wages; forcing up prices by taking advantage of the ignorance or hardship of another. (CCC 2409)

Secondly, it is a breach of contract. Whether this is a breach of contract primarily for the illegal distributor or the illegal consumer is debatable. However, any party privy to the existence of a terms-of-use or acceptable-use contract is morally obligated to uphold the terms of that contract.

Promises must be kept and contracts strictly observed to the extent that the commitments made in them are morally just. A significant part of economic and social life depends on the honoring of contracts between physical or moral persons—commercial contracts of purchase or sale, rental or labor contracts. All contracts must be agreed to and executed in good faith. (CCC 2410)

Thirdly, the Church teaches that divulging "trade secrets" is an offense against the respect for truth. Applied here, distributing or intentionally accessing the private 1's and 0's that support the livelihood or "private life" of business owners is sinful. And honestly, the best phrase I can come up with to communicate this concept in non-religious lingo is intellectual property.

Professional secrets—for example, those of political office holders, soldiers, physicians, and lawyers—or confidential information given under the seal of secrecy must be kept, save in exceptional cases where keeping the secret is bound to cause very grave harm to the one who confided it, to the one who received it or to a third party, and where the very grave harm can be avoided only by divulging the truth. Even if not confided under the seal of secrecy, private information prejudicial to another is not to be divulged without a grave and proportionate reason. (CCC 2491)

And lastly, it's not a bad idea to examine the practices of the moral authorities themselves. On the US Conference of Catholic Bishops' website, near the bottom of every page is a copyright notice:

© 2013 United States Conference of Catholic Bishops (usccb.org)

By participating in the copyright system, the US Bishops are clearly condoning leveraging of and adherence to copyright law. And the expectation is clear. If you want to use significant (complete portions) of content from their site, it's reasonable to assume that they expect it be to used only by their permission and according to their terms, per the copyright notice.

A final note: The Church also makes provisions for those whose livelihood depends on stealing.

The seventh commandment forbids theft, that is, usurping another’s property against the reasonable will of the owner. There is no theft if consent can be presumed or if refusal is contrary to reason and the universal destination of goods. This is the case in obvious and urgent necessity when the only way to provide for immediate, essential needs (food, shelter, clothing... ) is to put at one’s disposal and use the property of others. (2408)