My guess is that they come here because their own country sucks and they want to get away from it, but they don't want to do it legally 'cause (insert babies cries here) it's too hard and we'd have to pay taxes and we don't want to learn another language, or try to become a part of the society, we want you to conform to our society.
My apologies if I'm being too vague on how I feel about the subject
