Which should include pro-natal subsidies, but it wouldn't make sense to extend those subsidies to same-sex couples.

Agreed but it also makes little sense to extend those to any couples without children.

Same-sex and opposide-sex relationships are hardly comparable because of how different their behavior is. Straight people don't have the fetish cultures and the weird zoonotic diseases that gays do. Gay marriage didn't prevent monkeypox, did it?

The main issue is the production of children. Straight couples do indeed choose not to produce children and engage in various paraphilia as well, yet we as a society have little issue with allowing them marriage. I don't believe this is exclusively a homosexual issue.

The point I would make here is that homosexuality should be considered a paraphilia, as it had been prior to 1974, and that paraphilias tend to cluster together within an individual. Historically, most "gay" relationships were between adult males and adolescent boys, and this pattern is typical still today. Homosexuality is equated with pederasty as often by homophobes as it is by homophiles (see the "Kevin Spacey" defense for one example). While it's certainly not the only reason one would become gay, the self-reported rates of childhood molestation by older males in gay men is disturbingly high (probably around 50%).

This is definitely an elephant in the room nobody wishes to address. I think it's somewhat irrelevant to the question of legal marriage though. As that requires both parties to be well above the age of consent.

That last part is key. We can't have sufficient vetting, because that would be homophobic, and we have made it our civilization's existential purpose to stamp out homophobia (along with racism, sexism, etc.).

Agreed, the current culture is very much opposed to any kind of vetting or critical attitudes towards certain groups. This is also true towards straight couples as well though, even in conservative circles. I know people who adopted many children, and while typically adoption is something to be celebrated, people weren't always doing it for the right reasons. They were doing it for reasons of status within their religion organization oftentimes, oftentimes under the aspirations of converting as many children as possible. While I have no issues with religious people adopting and propogating their religion, theres a subtle but important difference between religious teaching, and cult like mentalities. The same exists within the gay community as far as I can tell. The activists are oftentimes insane, normal people are far more reasonable.