By asking for the “evidence to the contrary”, you imply that you do trust the source.
And if this were a one-time or one-issue thing out of Mr. Will, it may be considered an anomaly. But it is not.
Sorry, that's wrong. Whoever the messenger is, either the message is correct or it is not. If Barack Obama said that 2+2=4, the facts would be on his side and I would say that he was correct. That would not mean that I trusted the source.