if humans are rationale creatures why is overpopulation a problem?

Actually, the worlds population isn't growing as fast as it was before. So I would say that the human race is being more sensiable about how many they bring into this world. You also need to realize that Humans are also animals so those instincts are there no matter how hard you try and erase them. All that can be done is educate those that can be reached. Not everyone in the world has this privelge of education its getting there, still People have their own idea's and ways that they live and no matter the education, some just don't change. I could go on with this subject.. with the both sides of it. Knowledge doesn't always give way to wisdom.

By simply possessing knowledge will not change the way you act. You need to apply it and have wisdom. Wisdom is the application of knowledge so if they don't apply their knowledge it means that they are fool (opposite of wise). Humans know a lot of things, they know overpopulation by their decision to act properly is the problem. Knowledge is not enough. They should have wisdom.