On the contrary, do not ignore them. People base their feeling on the group opinion almost entirely on how often they hear a particular argument. They won’t remember that 90% came from 1 person.

Secondly, unless an idea is actively disagreed with, people (subconsciously) assume you agree with it.

Take every opportunity to disagree with the idiots. You won’t convert them, but you will sow seeds in the minds of those they might be swaying.