Is the principle of charity a moral or epistemological principle? Both, really, but it's often taken to be the former. If anything I'd lean towards it being more valuable as the latter.
The worst argumentative style of a group of academics I have ever come across is the critical realists. Their discursive style is one of eliminating an opponent. If caricature and defamation does that, all the better. (Okay, I suppose the above is a bit of a caricature itself but I'll stand by the assertion that there's a strong family resemblance between those who identify as critical realists and their discursive styles.) Bhaskar himself endlessly repeats the line about Hume once saying that there's no more reason to walk out of a front door than out of a third floor window (I've heard him speak a few times and he always wheels it out). Plainly that isn't what Hume meant, there was a broader argument going on there, but it's repeated on and on as if he was just an idiot. A nice, easy knock-down argument, as Humpty Dumpty would have said. We needn't agree with Hume (and I wouldn't) but making him out to be stupid doesn't constitute an argument, indeed it detracts from the arguments that are then presented (and in fairness to Bhaskar he certainly does present thorough arguments, albeit against straw-based lifeforms).
It's not so much that this style is morally objectionable, although this militancy can often degenerate into macho posturing, it's that it's epistemologically indolent. To take apart an argument while granting that argument the strongest, most reasonable interpretation you can honestly muster: that's a challenge.
I'm not against rhetoric in philosophy by any means but all too often it becomes a crutch for self-important hectoring. (Then again, so does blogging so I'll leave it at that!...)