Historically, it seems to me that marriage was (and still is in some primitive places) just another form of subjugation, more akin to slavery than love (for instance inter-spousal rape wasn't a crime in most states until the 1970s or 80s). The woman was passed from being owned by her father to her husband, and for taking on this "burden", the husband was compensated in the form of a dowry. Admittedly, I am from a household of divorce, so I think that my view on the topic has been soured, but I just can't find any objective reason why we still do this, unless its to pacify one's religious guilt, which, thankfully, I don't suffer from.
Though, at times you may be more inclined to leave a relationship if that "contract" wasn't in place. Sometimes, there is some light at the end of dark tunnels... you know what I mean? These days people hit a rough patch and scram, when anyone in a long term relationship knows that sometimes it's the rough patches that give a great friendship/relationship/marriage context and marrow.