But If You Go Back In Time ...
Set your time machine back just a few hundred years and you'd probably be surprised -- maybe horrified, if you're on the board of directors for Chick-Fil-A -- about just how many gay-married couples were running around in various places, remaining un-harassed by government agencies.
That would explain why the paintings look like Rainbow Marches.
In medieval Europe, which people mostly regard as the most prudish period in human history, same-sex marriage was pretty normal right up until the 1300s. The Christian church allowed them even if they preferred to dance around the sexual implications by referring to them as "spiritual brotherhoods." It wasn't until Byzantine Emperor Andronicus II outlawed gay marriage in 1302 that we decided that such a thing would surely ruin society if allowed.
In Africa, a 19th-century Nigerian woman named Ifeyinwa Olinke is well known for having a harem of nine wives (and one husband -- feel free to imagine what the sex looked like, you perv). And among the Nuer people of South Sudan, marriages between women are common, and if one of the women has children from a previous sperm donation, the other woman is unambiguously regarded to be the new "father."
"She loves it when I call her 'Big Poppa.'"