I don't know – do we have a record of the first marriage ever performed? Because it could simply be some ancient practice that pre-dates any established religion, but was simply institutionalized by them.

Then get a Civil Union. Same legal rights, without stepping on any toes.

Way I see it, the only reason they want it to be called “marriage” is for the sake of social acceptance. They want it to be recognized as the “new normal”.

For me, it’s similar to being on a diet, seeing someone on the same diet eating a donut, and then pointing out that while not necessarily a game-breaker, that the diet doesn’t really condone that.

Second party then calls you a bigot for daring to point that out, and then gets pissed at you, and the diet plan in general for not incorporating donuts into the plan.

Then point out that there’s a second plan that allows donuts, but technically wouldn’t be the same plan. It would, however, allow them to do things their way, without offending anyone.

They then reply that they don’t want another plan, because there are far more people on this plan than the other, and they want the social recognition of being on that plan, even if it means turning it sideways in order to accommodate them.

…But that’s just me.