There's nobody more annoying than the snob who sniffs, "Oh, I wouldn't listen to anything that so-and-so says."
The message they're trying to convey, of course, is, "I'm better than that person."
But what they're really saying is, "I need desperately to prove that I'm superior -- oh, and I'm very close-minded to boot."
Just about every time I've ever heard such an airy dismissal, I've wanted to reply, "Why not? So-and-so is a lot smarter and more realistic than you."
An argument should always be judged on its merits, not on the credentials of the person advancing it. And anybody who wants to judge a position on the basis of the education, or political stance, or job of the person advocating that position is only showing himself to be close-minded as well as dumb.
It's a little like the old Hitler-said-that line of logic: if a liberal hears a hate-fact, he says, in a suitably outraged voice, "Hitler said that!"
To which the best reply is usually, "Well, Hitler was a socialist, too. That doesn't seem to have shaken your political beliefs."
Or, "Should one not believe something just because Hitler said it? Well, Hitler believed in gravity. Should you therefore not believe in gravity?"
For some reason, airy dismissals, like Hitler logic, are things I hear only from liberals.
(Hadn't started out intending to make this post political, but somehow it ended up that way. Couldn't help myself.)