You remember where you learned things? That's remembering like, twice as much stuff! I'm pretty sure my brain is just making up plausible memories to fill in the gaps.
Ok let's just focus on the sciencier one for a second. Say someone doesn't like incest because it's bad for the gene pool. Their icky emotions about it predate religion.
That isn't a slippery slope to eugenics. Inbreeding depression is real, but eugenics is discredited as unscientific. We already know that rules against incest don't lead to rules against people with defects reproducing.
The problem with this line of thinking is that you're expecting people who support gay marriage to convince you about some other thing. And if any of these social taboos are actually a good idea, then you're lumping gay marriage in with them, like comparing gays to pedophiles.
Be careful, Hillary tried to create an easy opponent too. If we've learned anything from 2024, it's that desperate people will vote for any change. Even if that change is bad.
I generally agree with you, but I've heard reasonable arguments like
polygamy is patriarchy, gay marriage isn't
incest is bad for the gene pool, gay marriage isn't
These raise their own questions of how to dismantle patriarchy, or if governments should have a say in our genes, etc. But I don't think they're equivalent discussions.
I didn't like covid either but I sure ranted at people online about it!