My views on marriage are documented. While I think marriage as a legally or socially recognised relationship is redundant, marriage does make life easier for committed heterosexual couples, at least in India, and, I suspect, in most countries. (And that's the reason why I am married myself.)
Despite my cynical views on marriage, I often find myself taking the commitment of marriage very seriously. This is partly due to the fact that marriage carries exit costs (both in terms of legal and social repurcussions in case of a separation) and much more because of my belief that one's partner should be one's closest, dearest and most trusted friend. I would never advise you to stay in a marriage (or in any relationship for that matter) that you are unhappy in. The other side of the coin is I would ask you to be very careful while deciding whether to get married and not to enter into the relationship if you have the slightest doubt.
So here's my views on what are the wrong reasons for getting hitched.
Please don't get married because:
You are getting older. Marriage doesn't come with a use-before date.
You need sex. Get a lover. Better yet, learn to help yourself. And have some one-night stands.
Your relatives want you to get married. No, not even if they are hinting that your parents (or grandparents) are not getting younger or healthier and you should have a wedding while they're still around to see it. If you have to, buy a huge doll and stage a fake wedding so your parents can have fun.
You have younger siblings. Well, let them get married first. There's no law, I assure you.
You are lonely. Make friends. You can't expect your parents to keep doing everything for you. Seriously, this is a skill you should have picked up in kindergarten. (And if you find this difficult, you definitely aren't ready to take on marriage.)
You want to have children. (Seriously? Do you know how much work kids are? Oh well, okay.) Adopt a kid. If you need your own genes, have a kid with another single child-hungry friend and share custody. What if you do get married and then realise the two of you can't have children together?
You have been with your partner a long time. Have you ever heard of sunk costs? It doesn't matter how much time or effort you've put into your relationship. All that matters is whether the relationship is of value to you today.
So what are the right reasons for getting married? To my mind, there's just one: if you want to overwhelmingly be with someone else, if you want to spend most of every day with them, for the foreseeable future. (Better still, if you are already spending most of your time with them and want to make it easier to keep doing so.)