The reason people have sex before marriage is the fact that sex is just awesome.

And to most of your arguments I would say that not having sex is more likely to cause those than having sex. F.e. I don't think anybody ever got a depression cause he had sex. Many have one because they don't.

The HIV gets a point - but that is rather due to bad knowledge with sexual safety. And marriage also doesn't protect against HIV. Condoms do.