1. There are obvious legal and financial incentives which lead to our decision to have a legal marriage. You can easily share property, finances, death benefits, etc. Being able to jointly own property without doing a ream of paperwork as well as be on each others insurance was quite useful. After a few years our finances were already very intertwined and both of us had supported the other through periods of unemployment. It had become impossible to separate our personal successes and so we decided to essentially merge our financial and legal entities. Some married couples keep separate bank accounts and maintain a lot of separation, but we did not.
Also, a pair of people is far more stable than an individual. As I mentioned we have supported each other through unemployment and I supported my wife when she became ill. From a purely economic and social standpoint our marriage is a way to hedge our risks. I support my wife when she struggles and I know that she will support me if any ill ever befalls me.
2. We wanted to proclaim and strengthen our bond through a marriage ceremony. This was the reason we decided to do a social marriage. We felt that there was value in clearly proclaiming our intent to live together indefinitely in front of our family and friends. The act of clearly stating something out loud to witnesses can have a powerful psychological effect and it forced us to confront any doubts we had and think into the future to decide whether the course we were on was really one we wanted to pursue. Basically, the marriage prevented us from simply coasting into the future and forced us to make a clear and conscious decision about what we were doing and then we reinforced it by announcing that decision publicly.
So there are real benefits to having a marriage which are entirely non-religious. I do sometimes wonder about the gender issues and what is biological vs. rational. We do not plan to ever have any children, so our marriage isn't to provide a stable environment for them.
It is, but thing I would encourage people to keep in mind if they're wondering whether they want to participate in such a tradition is: Your marriage will be what you make it. No particular marriage has to be patriarchal, though of course many are.
You may choose, for example, not to have the wife change her last name; or maybe you both change your last names to something new, maybe by combining parts of your names (I saw this done once). The significance of that is symbolic, of course -- it expresses your commitment to an equal marriage; it doesn't absolve you of doing the hard work to make that a reality -- but it can be an important symbol.
You also might want to take a close look at the wedding ceremony itself. Using two rings is an easy step. The old tradition of having the bride's father "give her away" is one that I would suggest you might want to omit. If you can't bring yourselves to do that, maybe you could have the groom's mother also give him away -- people will laugh, but you'll make your point. Anyway, the larger point is, it's your ceremony, and you get to design it.
Can you have an equal marriage without doing any of those things? Of course you can, but if you find yourselves resistant to symbolic actions like these, you might want to ask yourselves why, because if you resist the symbols you will very likely resist the reality.
I'd like to hear more of that argument. Most specific marriage ceremonies are religious, of course, but I'm skeptical that the concept of (pledged) life-long monogamy and cooperative child-rearing has its roots in religion.
As for marriage being patriarchal, I don't really see how that's the case, at least any more than the entire world is patriarchal. I do suspect that monogamy comes from the selective pressure for males to have confidence in the paternity of their mates' children, so in that sense I suppose you could call it "patriarchal."
I am in favour of marriage for anyone who wants to have kids--which of course includes gay people and sterile people, thanks to technology and adoption--because it's a means of recruiting community support. Raising children well is hard, and the more people involved the better. Before the church got involved, this was essentially the purpose of marriage.
Some will still get married, even forward thinking secular people. There's a big difference between trying to build a family with someone who wants to partner up for as long as they're not unhappy, and having kids with someone who at least aspires to a permanent commitment. Marriage is pretty messed up in the U.S., but I still think it makes more sense to get married if you want to have kids.
Some won't. I don't think a culture built around transitory relationships is a good one for either parents or children. I wouldn't be surprised if there is a backlash in time, though I think another possibility is people just give up on having kids altogether. We'll have to see.
There are also some legal advantages in case the relationship ends with regards to income, assets, and child custody.