Killing them is more effective and much cheaper in the long run, If you feed them, you have to feed them every day, and then they go and have kids that you also have to feed. 

And before this post gets yanked for "uncivility," realize that I am answering a direct question from a person who believes that his straw man argument is actually intelligent; and go read Jonathan Swift. Yeah, I know. He's an old dead white guy. Read him anyway.