In Less Wrong/Slate Star Codex circles, it's called the Non-Central Fallacy (basically, trying to assert that a technically-valid edge case of X should be treated as if it's a typical example of X):

http://lesswrong.com/lw/e95/the_noncentral_fallacy_the_worst...

What's wrong with "bullshit" ?

I guess you're wanting both a more specific and more infectious (or virulent?) word, but: equivocation.