It's folly to suppose that they're not prone at all, but not so foolish to suppose either that their training makes them less biased, or that being less so biased makes people more likely to become scientists.

What I have been calling nefarious rhetoric recurs in a rudimentary form also in impromptu discussions. Someone harbors a prejudice or an article of faith or a vested interest, and marshals ever more desperate and threadbare arguments in defense of his position rather than be swayed by reason or face the facts. Even more often, perhaps, the deterrent is just stubbon pride: reluctance to acknowledge error. Unscientific man is beset by a deplorable desire to have been right. The scientist is distinguished by a desire to be right.

— W. V. Quine, An Intermittently Philosophical Dictionary (a whimsical and fun read)