Mark Spahn sent a link to this blog post by Jerry Taylor. It raises an interesting question: When is it permissible to question someone's motives? In a trial, lawyers try to impeach the credibility of adverse witnesses. They try to show, for example, that the witness has a motive (financial or otherwise) to lie, distort, or misrepresent. Ultimately, the factfinder (usually, but not always, a jury) will determine whether the witness is telling the truth. The jury wasn't at the scene of the incident, as the witness was, and so must rely on what the witness says. This is called testimony.
In public discourse, things are different. Most of the facts are "out there," accessible to anyone. There is no need to rely on anyone's testimony, as there is in the case of a trial. To question the motives of someone who argues that the globe isn't warming, or that, if it is, human beings are not the cause, is to mistake public discourse for a trial. The person making the argument isn't testifying about something only he or she knows; the person is reasoning from publicly accessible facts. The arguer's motives are therefore irrelevant.
As between progressives and conservatives, progressives are far more likely, in my experience, to question the motives of those with whom they disagree. This suggests that they view argumentation as testimony. That is a gross error. As for why progressives commit that error more often than conservatives, I have no idea. Perhaps it has something to do with their inability to engage in rational argumentation, which in turn may have something to do with the fact that they dominate academia, journalism, and the arts. (If you're never challenged, your argumentative, analytical, and critical skills atrophy.) Progressives are focused on people; conservatives are focused on arguments. Could this, in turn, have something to do with the fact that progressives are more emotional than conservatives?
Keith Burgess-Jackson, J.D., Ph.D. 