Why do today's Christians never express any kind of criticism against other religions?

Todays Christians generally agree that genocide is bad, that World War Two happened, that the good side won. And Jesus was not a time traveller.

Your question belies a deep ignorance about Christianity, Judaism and History generally.

Even just the fact that the Old Testament is the basis of Christianity (expanded with the New Testament) is very strange to me since it only talks about Jews and not Christians.

Christianity is a theological divergence from Judaism, the two religions share the same origin, that is why Christians refer to the Old Testament. It is a religious text that predates the New Testament; hence the moniker “Old” vs “New”.

Jesus was a jew because historical evidence suggests that everyone living in that time and place were jewish. There was no such thing as Christianity at that time, it did not exist. Jesus could not be Christian because he could not read a book with an account about his death because he had not died yet.

There is no credible text that indicates Jesus was a time traveller from the future who read the New Testament (an account of his own life and death), then travels back in time to fulfill the future timeline.

Jews and Christians worship the same God. The Old Testament includes ‘Genesis’ the story of creation. Where God created everything, if Christians reject the Old Testament they have to devise a new creation story.

"Back in the day", I get the feeling that they had a quite different perspective. What has happened in recent decades?

“Back in the day” you might be referring to the holocaust.

Yes during the holocaust there were many Nazi who made manipulative and deceitful statements about Jews to turn the public against them. The purpose was to recover economically. Germany could rob a significant portion of their own population through a systematic campaign of murder and then gain power by warring and dominating other nations.

In “recent decades” people have generally come to the viewpoint that the holocaust was a human atrocity. And that murdering people due to their religious affiliation is morally reprehensible.

Maybe there is some kind of Christian branch which does have such criticism, but if they exist, I have certainly never been able to find them.

Yes a Christian branch did exist with a view that Jesus was not Jewish, that branch existed in Nazi Germany. Hitler attempted to redefine Jesus as an Aryan.

During the Third Reich, German Protestant theologians, motivated by racism and tapping into traditional Christian anti-Semitism, redefined Jesus as an Aryan and Christianity as a religion at war with Judaism. The Aryan Jesus, by Susannah Heschel

There maybe quasi Christian groups that continue to follow these teachings; however that Hitler (a notorious figure) is the principle inventor of this branch of Christianity is generally repulsive to people aware of his role in the genocide of millions of innocent people.

It is unlikely then that an ahistorical, debunked, recently invented account of an Aryan Jesus would be propagated on radio.

Todays Christians are more likely to align with the prevailing view that Jesus was a jew, than the Nazi view that Jesus was an Aryan. This is because some time ago the Allied powers mobilized nearly every man across earth for a time to murder millions of Nazi’s.

Today most Christian learn in early school curriculum about WW2 (the largest theatre of war ever), and their nations role in preventing a world dominated by Hitlers ideology.

I think the answer would be because they are Christians. As such they should be focusing on correct doctrine rather than dissing religious groups, and they should do so in a Christ like manner. Sometimes some religions are so diametrically opposed that you will find criticism inevitable and it certainly exists in a number of cases.

I have noticed that Jehovah’s Witnesses do cop a fair bit of flak from most other Christian believers, including here on CSE. They have in some cases fairly divergent beliefs, though they share many others in common with other Protestants. I have never been comfortable with the criticism they face by simply being Jehovah’s Witnesses. Certainly I disagree with and do point out issues in their beliefs but hopefully in a manner that still portrays a Christian spirit. And in saying this, in this way, add strength to the argument of why Christians are not that combative, or at least should not be, towards other faiths.

I do however agree with you in that most of the Protestant movement have lost much of their vigour in opposing the Roman church over the last 500 years. In fact many of the Protestant religions are now working hand in hand with the See of Rome or at least welcoming them in ecumenism. A far cry from the strident and vehement criticisms of Martin Luther and his reformation contemporaries.

Likewise the Roman Church has also significantly altered its stance against Protestant Religions. 500 years ago it was burning at the stake any Protestant it could lay its hands on. Even the anathemas have mostly if not entirely ceased.

The only way to God and the only mean of salvation is through Jesus Christ (John 3:15-16; 14:6), God made flesh (John 1:1,14; Philippians 2:6-7; Colossians 2:9). If someone does not have (or despise) Jesus, neither will have the Father (God) (1 John 2:23). Maybe they could worship and pray to a god, but it wouldn't be the God of the Bible. This include all religions (Judaism, Islam, Buddhism, Hinduism, Atheism, ...). Having said that.

The main concern of Christians should be the teachings of Jesus Christ and the aplications for our lives. Depending on the background they might focus on particular subjects influenced by where they live or the growth of the congregation, for example. In the West, perhaps, the focus will be more on cultural issues such as abortion, feminism, LGBT or communism, but in countries with a majority of other religions (or with an expansion of a particular religion), they could expose those believes, defending our faith, sharing the gospel and making disciples.

The reasons for not talking about other religions can be several:

1. Fear of retaliation,
2. comfort, apathy or postmodernism,
3. fear of being judged or believe that it is wrong,
4. they see it as not essential or unacceptable,
5. not estimating the truths of Scripture as fundamental Truths, or
6. simply lack of knowledge of a particular religion.

My experience has not been similar to yours, in that I do hear church leaders criticise other religions. In addition, as a young man I don't know what things were like a few decades ago to compare it too. Nevertheless, I want to attempt to answer the question.

This article, from a prominent Evangelical source, discusses the way in which the author suggests Christians interact with other religions. While we could debate whether the author is correct, I would say this is a common view. The author generally tries to hold together two opposing views: a) belief in Jesus is the only way to salvation, and therefore we must criticise other religions, b) we must do so in a way that helps our cause, rather than hinders it.

The Apostle Paul says a similar thing in Collosians:

Be wise in the way you act toward outsiders; make the most of every opportunity. Let your conversation be always full of grace, seasoned with salt, so that you may know how to answer everyone. Collosians 4:5-6 (NIV)

Exactly what being wise and gracious means will depend on the circumstance, the people involved, and the nature of the society we live in. I suspect every Christian will have a different idea were that line is, and I've heard many say our modern (in particular, Western) Christianity are a bit too generous with this line.

However, I understand why a Christian radio station in particular would choose to avoid criticism of other religions. They have chosen to perform a particular role, and leave other functions up to the church. For comparison, consider the way this Stack Exchange runs. Two thoughts that immediately jump to mind:

Firstly, a public radio station needs to cater to a wide range of Christians. There are denomination here on Christianity.SE that I strongly disagree with, and feel ought to have their beliefs criticised - but I recognise this isn't the platform for doing so.

Secondly, a pubic radio station has no ability for personal discourse. If I disagree with the pastor of my church, I can go talk to him after the service (and on occasion have done!), and he can get to know my particular objection and life situation. A radio broadcast doesn't allow for this. Again, this SE has made similar decisions, albeit about a slightly different topic.

In conclusion, I would say that the reason some Christians publications choose not to openly criticise because:

1. They believe there is biblical precedent for being wise towards other religions
2. They believe in our current climate, "wise" means avoiding public, impersonal criticism
3. They have chosen to perform one specific function, and leave the rest of the church's responsibility to the church.

Whether one agrees with this logic, I would say that is the decision being made. I would hope that an individual church would recognise the need to expose the un-truths in other religions, and would seek to do so in a clear but wise manner.