There's explicit scripture in Acts where Peter has a vision saying that food is all ok. That's why we eat bacon.
Christian reasons for doing most things aren't legalistic, it's because we believe that's how we were designed. We believe God designed sex to be a part of marriage, and to essentially save us from ourselves. Sleeping around is the cause of a lot of pain, so God's like "Hey. That makes things suck for everyone. Maybe don't do that, yeah?"