Upvote:1
To your first bullet point, how could masturbation be a sin in one language, but not another, due to a simple technicality of linguistic definition? The act itself either is or is not sinful. It doesn't matter which language you use to talk about it (although linguistic difference may affect how you talk about the issue and clarifications that need to be made).
The simplest answer as to why masturbation is a sin is that God did not design the human body for masturbation. Jesus says that in the beginning, God created them [us] male and female. Sexual acts are not complete divorced from this male/female context. Furthermore, it is evident that God created sex for procreation, and for marriage. To do sexual acts outside of procreation (at least an openness to life) and marriage, therefore, is clearly wrong. Masturbation is a sexual act which takes place outside of both contexts; it is neither within marriage nor is it procreative.
Edit: I've got a note here asking for a credible source, as if it isn't just common knowledge that this is the Catholic teaching on sex. Here is a source: https://www.usccb.org/issues-and-action/marriage-and-family/natural-family-planning/catholic-teaching/upload/Openness-to-life.pdf
Upvote:2
Man was made for woman, and woman for man. Sexuality is meant to be a coming-together of two parts which make a better whole (Genesis 2:18-24). It should be clear that adultery tends to damage this relationship. Moreover, sexual perversions (p**nography, h*m*sexuality, be*t**lity, masturbation, etc.) are all ways of seeking sexual pleasure outside of this intended relationship. They are, in effect, a rejection of God's intended plan for humans. Some would also argue they are a rebellion against God's command in Genesis 1:28.
That said, the Bible also commends bachelorhood, which would seem to argue against the idea that not having children is in itself sinful. Even in that case, however, the argument against God's intended way for sexuality to be expressed still applies, as do all Biblical commendations to sobriety. In that respect, masturbation (and p**nography) are similar to drunkenness, in that they become pursuits that distance one from God.
there is no formal definition for sexual immorality
There are at least two definitions which are widely used:
In my experience, the former believed rather widely among Christians and seems to have good Biblical support. The latter is an even stricter definition which is held by some Christians, particularly Roman Catholics.
Masturbation is a pursuit of the pleasures of the flesh outside of the means which God has established. It is an act in which does not glorify God or conform to any expressed intention of God, wherein one is focused on self-pleasure, and often corresponds to a lack of self-control. There are many Biblical teachings admonishing the Christian to exercise discipline over his or her own body. It may also represent a sort of "end run" around a relationship which God desires (that between husband and wife).