I love this class of "logic" employed heavily in... well, just about anywhere where there's an "us" vs. "them" mentality, particularly in politics:
Fact: Person X [on the other side] did Y
Assertion (assumed to be true without proof): Person X did Y for reason/objective Z [invariably bad]
Fact: There's no way Y could accomplish Z
Conclusion: Person X is bad, and an idiot, too
Uh huh. Maybe when you can come up with a reasonable explanation for your opponent's behavior other than a set of vices (greed, stupidity, cluelessness, just plain being evil, etc.) I'll take your politics seriously (note the subtle implication that I take few people's politics seriously).