Here is something from the New York Times's "The Stone" (Jason Stanley of Rutgers writing) worth considering:
It is naïve not to expect that the practice of politics demands some amount of assertion that is for purposes other than conveying the truth. But reasoned debate presupposes mutual knowledge of sincerity.
(Read the rest). I'd agree on both counts. The piece focused on the problem of insincere speakers, but the same point might have been made about listeners who won't accept others' claims to sincerity. In a lot of ways, that would be worse.