I have a self-image of having badly sub-par social skills, and have a fair amount of evidence to back up that image.

Like what? BTW, have you heard of the impostor syndrome?

On the other hand, I note that I currently have 95% positive karma. If I lacked the capability to avoid alienating people, I would expect much more negative karma.

Alienating people may be easier in meatspace than in writing, depending on lots of things.