Homosexuality is a sin, because ancients believed Semen was sacred, so 'wasting semen' was considered a sin, this is why Catholics teach that masturbating is a Sin.
Magus,
As always, you bring an interesting perspective. Have you considered that homosexuality and masturbation (along with all other sex-related sins) are considered sinful because--within an orthodox and traditional Judeo-Christian context--God created sex acts to occur, and be enjoyed, only within the very narrow confines, sanctity, and protection of a formal marriage between a man and woman? (You know the scriptures well enough that I dont' need to cite all the supporting verses for this traditional interpretation, and more recent efforts at reinterpretation are outside the scope of this exchange.)
A Catholic doctrine of Sacred Semen is an interesting concept, but--if you really look into the issue--I think you will find ideas of lust and selfishness and a sex act outside its God-dictated context as more compelling reasons for the prohibition on masturbation. (And if you want to argue that these ideas were mapped on later, please clearly cite your sources and clearly identify and separate out your personal analysis. Your input is always intriguing, always adds flavor, but your arguments are often so esoteric (albeit fascinating) that it is hard to sift out your personal conjecture from source material.).
Do Catholics proscribe female masturbation? (I don't know...but if they do, how does the Sacred Semen idea apply?)
Leviticus 20:13 - If a MAN (masculine) , it didn't say anything about Lesbians.
True. If you flip ahead a few pages to Romans 1:26-27, you'll find more on the issue:
"Because of this, God gave them over to shameful lusts. Even their women exchanged natural relations for unnatural ones. In the same way, the men also abandoned natural relations with women and were inflamed with lust for one another."
Here it uses "shameful lusts," not "sin," but the tone and meaning are pretty clear. Could you argue that this first sentence is referring to bestiality? Sure, if you disconnect it from the second sentence and look at it out of context. That second sentence uses clear language tying them together, however ("In the
same way," "men
also abandoned...). Both sentences have all the appearances of talking about the same thing--homosexual sex.