Which passage of the Law, or other Scripture, defines which group a particular provision falls into? Or is this distinction you find so compelling based on anything at all besides your personal preference?"
Well, no, I didn't sit here by the window and make it up. It's a traditional view which goes all the way back to the Westminster Confession of 1643.
So where did you get the idea that Christianity doesn't prohibit homosexuality?
Care to go back and quote where I said any such thing?
The New Testament clearly prohibits homosexual behavior and all other sexual activity outside of marriage. Between a man and his (female) wife.
My point was that the Bible (both Old and New Testaments) do not produce the distinction between homosexuality as uniquely evil compared to all other forms of sexual immorality. The standard I believe in is actually higher, since it requires abstaining from heterosexual as well as homosexual immorality.
So of the 613 (or whatever) laws in The Law, somebody sits down and places each in either column A (ceremonial) or column B (moral). Since no such distinction is specifically found in the Law itself, and the two groups are intermingled throughout, as shown by Leviticus 19, it means somebody has to decide which column to put a law into.
Which means the question arises, who makes that decision and on what basis? And what scriptural reason is there for not later deciding that the prohibition against homosexual acts should not be reclassified as ceremonial rather than moral? Other than personal preference, of course.