Why do we find ways to hate the opposing party?

Why are people so hostile about each others' political party? I am conservative and believe much in the ideals but that doesn't impede me from respecting a liberals ideals. Why do people get so pissed off. Are all of you aware that no matter what we have-- Republican or Democrat-- we are all screwed? What's the point if both parties are going to lie to us and make us look stupid for sticking up for them in the first place?