I agree with part of what you say. Sometimes if you have sex before marriage, these things happen. I think people should wait until they are in a committed relationship.
I did have sex before I got married. In fact, I lost my virginity at 21, but we had talked about marriage before hand. We became engaged a few days afterwards, and ultimately decided to move our wedding date up and got married three months later, and I couldn't be happier.
Not everyone in the US is having sex causing these problems, and the US is not the only country causing these problems. And marriage doesn't automatically make having children okay. If someone is married it is far harder for them to leave an abusive relationship, a relationship that they shouldn't be in and shouldn't be bringing children in.