1. If I make a spelling, grammar, or word choice error, or am unable to find a noun and have to describe the thing, then my entire point is invalidated. If I fail to accurately translate my shapeless, interwoven web of thought-color-shape-idea into paragraphs the other party can understand, they now have reason to regard everyone who holds my position as too stupid to be allowed to speak.
2. Insisting on a debate can be sometimes (but not always) a tactic used by people who want to wear out the other side.
3. The same reason I block, mute, and ignore advertisements: I get to decide how to spend my attention.