I think you also posted on a daily thread...? Anyway, this post is late, so I don't know how many people will see it. And I can't respond to OP since it was deleted.
I used to be really against marriage. Between my parents, they've been divorced three times. Messily. I'm staunchly non-religious. Plus, weddings can be kind of expensive. Plus, what's the point of "tying someone to you"? Two people should only be together if they want to be together, no more, no less.
In fact, I told my now-husband on our first date that I didn't plan on getting married. (This resulted in me being the one proposing, which is also good, because it meant we didn't have to spend money on an engagement ring.)
It's a cliche: I changed my views when I met the right person. Which is to say, I felt secure enough in my relationship that I was no longer worried about divorce. (You may call me naive/optimistic, if you'd like.) I felt it was worth going through the motions of a wedding ceremony (which doesn't have to be that expensive) in order to give my now-husband the legal protections as well as the social acceptance.
Yes, society treats married people better. Is that right? Not really. But it's a fact. And it's something I can do for myself and my partner.
But anyway, with regards to FIRE, it's not really related. My goal in life is to be happy. Being married to the person I love makes me happier than any amount of money. (Yes, even if it's the PowerBall lottery, at its height.) It's worth it to me to work extra years, if it means that I get to spend those years being with the person I love.
For me personally, being married (to someone who makes less than me) has only accelerated my track to FIRE. Four years ago, when we met, I had a net worth of $100k. Now, we have a net worth of $650k. Also, because I couldn't cook or do anything domestic, our annual spending basically remained the same even though we are now two people. (It increased because we go on more vacations now, and because we donate to charity more now.)
If you're happy not being married, that's great. (In fact, I think everybody should learn to be happy being single, before they get into a relationship, even if that's the eventual goal.) If you're only against marriage because you think the risk is not worth it--well, I hope you get lucky enough that you meet someone who changes your mind.