And indeed we (people) did. There are just billions of us.

My proposed revision of the conventional wisdom:

 "Don't go out and have sex until you are   emotionally and financially ready to take care of a child." 

I got plenty downvotes for staying "sex is about reproduction." Attention: making babies is the purpose.

The recreational, entertainment side of sex is merely an inducement. A lead in. Not the purpose. If you think otherwise, you are likely to get stuck.