Taking the easy way out

I was going to post this in response to a comment to my previous post, but I think it has some general relevance:

Can we put an end to the disingenuous practice of trying to discredit a writer’s opinion on one specific subject by quoting (in or out of context) his or her questionable opinions on other subjects?

This practice, of course, is not restricted to any political or ideological grouping. And before anyone starts searching the archives, I’m sure I’ve been guilty of it myself.

Are Marx’s genuine insights about capitalism discredited by his racist and antisemitic remarks? Are Orwell’s great essays and books valueless because because of his sometimes retrograde comments about Jews, feminists and birth control?

If you want to challenge an opinion on its own merits, by all means do so. And of course a writer’s own inconsistencies are fair game. But instead of explaining why writer x was wrong about y, a number of our commenters take the easy way out by saying “Writer x was wrong about z, so how could he be right about y?”