It's really hard to walk away from being told you basically suck and know diddly squat about writing, let alone the entire science fiction genre (which is, of course, only the gee-whiz high-tech type of story, otherwise it's not *really* SF, just wearing an SF skin and "might even be called sci fi" (but not actually be SF, of course.))

Sorry to threadjack, but this is EXACTLY when you have to walk away. You know there's no way you've missed the mark that badly, he has nothing constructive to really offer, and you're mad.