"My word, immorality is not a good enough reason to ban sodomy?"
Your distaste for such an act does not impress me. You are not the arbitor of morality.
"If morality is not the bedrock of our laws, then they all rest on shifting sand and we might as well recognize as "normal" adultery, polygamy, prostitution and the like."
But who gets to decide what isn't moral? You? I don't think so.
I might point out, the Bible, which many view as a moral guide, says nothing against slavery, polygamy, prostitution and often condones adultery.
"After all, proponents of these aberrations have as valid a claim to discrimination as do homosexuals."
Salvery and polygamy can fairly easily be shown to have negative effects on societies. As long as prostitution is truly a choice I see little wrong with it (not that I'd be going that route.) And, though adultery probably most often has a negative effect, it would be much too difficult to fairly prosecute to bother with laws against it.
I put it to you to show credible evidence showing that homosexual "sodomy" has significant negative effects on a society.