Off late I hear quite a lot of young people who don't seem to be believing in the institution of marriage. It could be due to the fact that they see increasing number of divorces or could be due to the fact that what they could do only after marriage before (sex), they can freely do it before itself. I am saying freely because I see quite a lot of live-in's lately. I am not saying its wrong or its right.
Marriage is the union of two souls which is generally presided by a priest. Elaborate arrangements are made and elders in family and friends bless the couple for a life time of happiness. It marks the beginning of a named and recognized relationship.
Vows are exchanged in front of fire marking that you are promising in front of God that you will Honor, respect, protect and love each other until end (death). This is the main difference between girl friend and a wife. So, it is safe to assume that we get married for spiritual reasons more that anything else.
If you look around, people who are Atheist's also get married. Mostly they do it to to let the world know that they are a couple. I think, correct me if I am wrong. Some get married for tax purposes.
In case of court marriages, even though the wedding takes place on papers, most couples do in fact get at least a small puja/prayer done for them asking for the blessings of God.
Whether it is old days or modern days, Marriage still is a very important part of our society. Whether one wants to get married or not is a personal choice but denouncing it certainly doesn't seem right or natural.