The tone, the mean-spiritness, discussing posters instead of issues. Even if you don't start that way, you become what you try to resist as a matter of survival. But some are quite mean.
However, some people just cannot deal with politics due to disagreement and probably avoid it for that reason.
“The power to declare war, including the power of judging the causes of war, is fully and exclusively vested in the legislature.” ~ James Madison, Father of the Constitution