You are very well schooled on the names and intracies of logical fallicies, but your resort to unfounded opinion to support your arguments. The argument you make above might be called the "That's so outrageous it could never happen" fallacy. Going back 50 years and coming forward, we could reference a string of "experts" explaining to us how out of wedlock pregnancies, the homosexual agenda in public education, animal rights, multiculturalism, a sex scandal in the White House, etc. would never become accepted as normal. The ongoing breaking of moral barriers has become normalized. People have come to accept that "morals are declining." Observation tells us that morals are, indeed, declining. It's only logical to assume that they will continue to decline - meaning that what is immoral today will become acceptable tomorrow. Another word for a decline is a slope. A really steep decline might be called slippery. The only correct thing in your nit picky list of fallacies is that we can't accurately link correlations to causality - we don't know which norms will be the next to fall. But we can guess. It doesn't take a degree in linguistics and logic, just a memory and a little common sense.
Thanks for saying what I am too PO'd to say coherently.
I believe the characterization of a 'slippery slope' moral argument can be either valid or invalid, depending upon the particulars.
Our rationalizing friend imagines that syllogisms have more substance than reality itself; he is wrong.
Remember, dimensio, analysis of terms yields tautologies, at best.
All actual truths about the empirical world around us are rooted in observation, not analysis.
I think I know a slippery slope when I see one, so spare me your argumentum ad misericordium.
The truth may make you unhappy, but it's better to be unhappy than ignorant.