Again, it's tough to explain unless you have a frame of reference of having been in a relationship where the M word isn't a scary thing.
Neither my husband nor I are religious and we do not believe in much of any of that hooey anyway. So why get married? Well there's the legal stuff of spouse's rights - I'd much rather trust my husband to know when to pull the plug and vice versa. I'd much rather him inherit all the stuff that I forgot about in my will, rather than it going to relatives I don't know, I'd much rather it be him to have the first say about my wellbeing in the event that I'm unable to myself. If we did not have that, then my family could fly here and take charge and perhaps do things that while they think I would want, he would know I wouldn't, but he would have no say without the marriage bond. Vice versa for him.
If you don't get married or set up a legal partnership, you don't get any of that, including any tax breaks and such.
But that's the pratical stuff. The rest is intangible and tough to describe to someone who has not found a partner like that to go through life with.
It's true you can do it without the church ceremony. Certainly we didn't go to a church, you can (depending on local laws) get a legal partnership that means the same thing. That's what my husband's brother and his wife did. I say wife because in this country if you say partners they assume it's same-sex, and she wasn't his girlfriend, his lover, his SO, they were a couple and a team, and everything that a marriage is. They had the legal paper to prove it but they didn't go the marriage route. It all meant the same thing legally and otherwise though.
So yeah the parntership can be an option, but marriage isn't exactly meaningless even to the unreligious.
