As to recent trends, it’s far from a uniform shift globally. Uganda joined made homosexuality punishable by death just last year. https://en.wikipedia.org/wiki/Anti-Homosexuality_Act,_2023
Going back another 20 years. 1991 Iran declared homosexual gay sex as punishable by death.
Saudi Arabia has verified executions for homosexuality as recently as 2019.
etc
The historicity of "same sex unions" of Roman emperors (Nero, Elagabalus) is debated. These claims may have been recorded to discredit those emperors.
There was no legal recognition of same sex marriages or unions in ancient Rome.
In terms of legality of marriage in Rome, I mostly agree. Arguably male adoption of other adult men could be largely equivalent to heterosexual marriage as far as the state were concerned. Ie name change, social rank, and property as there’s no kids and no wife possibly leaving her father’s control depending on the type of marriage. To be clear it was often a political tool, but that doesn’t mean it was always a political tool. Just something to think about.
Even Sodom was about raping angels, who appears as children. Note that rape is definitely not consensual sex.
Marriage, as far as I can tell, is a concept that originated in different places with multiple definitions and the scope of what can or cannot be marriage has expanded and contracted over the years.
Marriage often has legal and financial implications. Those who want homosexual marriages probably want to also benefit from those. There are also non-trivial symbolic reasons. In this context I am using marriage and civil unions synonymously.
This is probably the best case against gay marriage, because it could easily just be about civil union that is acknowledged by the government and granted the same benefits, without needing to call it marriage, which should be the matter for each religion to decide.
Religion is a social construct which has co-opted various parts of life, not the other way around. It has no right to dictate to society what is allowable, only government has that right, given to it by the people themselves.
Marriage is a legal agreement that gives the parties certain rights and responsibilities that single people do not have. Historically governments have discriminated against homosexuals just like they've discriminated against other minorities. Discrimination is wrong. That religion promotes discrimination doesn't excuse it.
Some people think homosecuallity isn't acceptable, but it's something that occurs naturally in various species, including humans.
Arguably religion came before government, with early governments blurring that line. If so, then religion was the first to formalize reproductive union for the purpose of growing your group's population.
I think early humans probably discriminated against sexual activities that didn't promote reproduction and building a family because there weren't that many people back then, so not reproducing could mean the end of your civilization.
I think this is making too much of a distinction between religion and government.
For most of human history, most humans were not privy to clearly-defined centralized institutions (like our modern state bureaucracies). Religious traditions were decentralized emergent phenomena that codified ways of perpetuating a functioning society in a low-trust, low-organization environments.
As far as marriage specifically goes, it evolved as a practice in order to make the process of material inheritance simple, nonviolent, and easy for anyone to execute. This is where the notion of "legitimate" children comes from: legitimate in the sense of being eligible for inheritance, specifically because your parents were married. When strong centralized states started emerging, they codified this practice and built new structures on top of it.
At a personal level, I have zero pressure from society to reproduce and I suspect this is the case for millions, and because the problem spans across generations, it becomes invisible to people who are currently alive. This is what religion addresses that science may be incapable of. Now in post-modernity, we are embracing this miopic perspective at the risk of our civilization. Maybe 200 years from now the world will be 100% Muslim, and the Enlightenment will need to re-emerge, only to restart this cycle once again.
I don't mean this as a flippant question - I think it's at the heart of the matter.
Governments can decide that a homosexual union can be called marriage.
Religions can decide that a homosexual union isn’t marriage.
But Religions can’t expect others to accept their definition. They don’t get to demand that the government accepts their definition, unless they can get the votes.