Hey Catz, are you Catholic by chance? You sound a lot like me when I was 12. I used to be Catholic and believed that sex was a sin. But then I realized, if sex is a sin, then God created us to sin as a necessary part of our reproduction process. That didn't make sense to me, because whatever preachers tell you about fire and brimstone, I don't think God would be that mean, "God is love" after all.
There is being a sexually active, responsible adult, and then there's being promiscuous or too young and naieve to be physically involved with someone of the opposite sex. I can't find anything wrong with the former scenario, the last two scenarios are people being irresponsible. People can be irresponsible with just about anything, money, food, prescription drugs, alcohol, their own opinions, etc. and sex can certainly be misused as well. This is more a matter of people doing stupid things than sex being evil.
Some people use the argument that sex is only sin outside of marriage. But what about before marriage existed? There is no evidence for any ritual similar to "marriage" in the prehistoric caves where early humans painted animals on the walls. In fact, the earliest recorded account of marriage was only 5,000 years ago. Human beings have existed for 200,000 years. Does this mean that God gave man no way to live in purity except going extinct? I don't think so. I think marriage is a human creation, just like circumcision and funerals.
So then, there really is nothing wrong with sex, just as there is nothing wrong with eating or thinking or anything else human beings do out of necessity of survival and growth. Living a life of abstinence is a great way to find inner peace for some people. I actually considered becoming a nun for a while, but thought that I could help more people outside a convent. If you desire a life lived in chastity, then more power to you, that is a noble choice. But for those of us that have not chosen that path, let us be. Our children will be the future of the human race.