Yeah, that's a good point about Christmas. I guess the reality of whether something is religious or not really just depends on the way that it's practiced culturally. I feel like the majority of marriages still involve altars and vows and all of the Christian trappings, so I think that they have a lot more of their original Christianity retained than Christmas does... Especially since the most iconic elements of Christmas were pilfered from earlier religions (which probably contributes to why Christians don't want to complain about it that much).

It really is as simple as just having a clear distinction between secular and religious marriage like you said. I think that if someone is licensed to perform a legal marriage, they should not be able to turn down a customer on account of them being gay. But I do agree that a religious marriage should be able to turn down gay people. The problem of course, is that the boundaries between the two are so muddied - and it's only the Christians that are doing the muddying. I used to be more of the " let them do their own thing" type of atheist, but I think the real key thing to watch out for there is that a core tenet of most religions involves spreading itself to others whether they like it or not. They believe they have a moral imperative authority over your private behavior. It kind of reminds me of the bugs in Factorio if you've ever played that. Like, at first it seems fine for me to just let them chill and breed their little hive off in the corner of the map, since we both leave each other alone. But the problem is that the intrinsic nature of those bugs is that they'll eventually come and fuck up my factory - they can't and won't leave me alone. When it comes to Christianity at least, I've started to see it more like this:

If they're leaving me alone right now, it's just because they're incubating power to force upon me later.