It's good in life to find SOMETHING you are committed and loyal to. Otherwise you're just going to be blown about with the wind with no sort of foundation in your life. Now it's good not to bog yourself down with too many commitments so that you're inflexible, but there's such a thing as being too flexible. It's probably best to strive for some kind of middle path.
What you decide to commit yourself to is your business as long as it's not criminal. Some commit themselves to duty, some commit themselves to a belief of some sort, and some commit themselves to family. Some try to commit themselves to all these things, and I suppose it's possible when they don't overlap, although it really hinders flexibility.
Real actual marriage is a commitment to family, although it's tough to tell nowadays since so many don't honor their commitment. When you sign that piece of paper, or do the ceremony or whatever, you're saying you're going to stay with your new family no matter what. When times get tough, you're not just going to abandon your wife/husband and play back and forth with your kids. If you have doubts that you can honor the commitment, don't go through with it. But many do anyway, either because they take the commitment too lightly, or because their spouse ends up abusing them and they couldn't foresee it. Most of the time it's probably due to a light commitment attitude. And they probably just do it for appearances and a fancy celebration. Bad, bad reason to get married.
Whether you get married on paper or not, I don't care. But I would say, let your promises be true. I would think, if you truly cared enough for the person to live the rest of your life with them, you would say so even if you don't get married. There are going to be relationships you have when you probably don't feel that way, and that's fine. But I do think it's nice to find someone you can grow old with. If you don't want to grow old together in your current relationship, I recommend you don't have kids with the person you're with. Kids are not a short-term thing, and while they're tough and can handle being with just one parent if necessary, I bet it puts them in a bind when you start fighting over who gets to see them when.
If you can't stay committed, adopt a child in your name only. That way no one can fight over them, and you know whose child is whose. If you don't want to have kids, yeah, marriage may not matter, in verbal or in ceremony/legal form. So I guess marriage is ultimately an agreement to share any children you have together and not try to steal them away for yourself.
Personally though, I love romance, and were I not in a forum where everyone hated marriage, I would describe it much differently. I hope everyone that desires to find lasting love does so. Those who want a life of bouncing from one relationship to another, I guess I wish them that. I just don't know why that would be their desire.