Exactly right (that if you can't argue against a position without considering its source, you likely don't have an argument in the first place), but note that this has been roundly ignored in public discourse for years. It had gotten so common by the 1940's that C. S. Lewis felt compelled to make up a name for it - he called it Bulverism. Others have come up with their own monikers for it (Anthony Flew referred to it as the "Subject/Motive Shift", and it is more generically known as the genetic fallacy, or a motivational ad hominem). The technique is basically, don't bother trying to prove an opponent is wrong, just assume they're wrong, and "explain" what motivates them to say what they do. It also involves what I am beginning to call the 'omniscient imagination' fallacy, as there never is given any real evidence for the proffered motive, it is just assumed that if I can imagine that motivation, it *must* be true.