I think a big part of the problem is that people tend to assume that being polite means being passive and non-confrontational - in all sorts of areas, from politics to dealing with a man getting handsy. We aren't taught how to be assertive (or how to detect and dismantle false arguments) - only how to be compliant or aggressive, neither of which is healthy.
Our church used to host a Meet The Candidates ahead of the general election, and a certain decency of speech was expected, but if a candidate was so discourteous as to ignore the bell announcing their time was up, the person at the sound desk would cut the microphone, and the big burly moderator would retrieve it.