Why should someone have sex before marriage?

Sex before marriage is both dangerous and wrong for a multitude of reasons, but I know many people (especially on Yahoo Answers) disagree. I'm willing to give them a free, open forum to counter this claim. I want to hear the most logical arguments out there for why sex shouldn't be saved for marriage. And just a word of warning, unkind or immature comments won't help your cause, so be civil. Here we go ...