The greatest reason (other than the Commandment) to avoid sex before marriage is: once you have sex with a person outside marriage, your judgement becomes so clouded you are incapable of accurate evaluation of compatibility. It becomes far more difficult to escape the relationship, even if you know that would be better, because of the selfish reason of easy sex.
Once you give up your virginity, sexuality really gets in the way of seeing the more important factors in choosing a mate.
This is so true. I saw this first hand. People underestimate the destructive nature of illegitimate sexual relations. It can turn the most sensible person into the most irrational, illogical being. Good article.