Why are my opponents ignoring what I say because I said it angrily, or sadly, or confrontationally, or in passing, or whatever?

The way you say something may signal that you are trying to diminish their status. If you say it with a sufficiently negative tone, it may even be taken as a signal (a generally reliable signal) that you care more about diminishing their status than about having a truth-seeking discussion.

In other words, what wedrifid said, but less simply and more explicitly.