You are right on all fronts. Writers who disable comments are missing out on positive feedback and helpful insights, too. I have benefited a time or two for readers pointing out errors. I misspelled Colosseum because spellcheck didn't pick it up. I was so grateful someone pointed it out to me, because I able to fix the typo and save myself further embarassment. Those who ditch the comments section also missout on the hilarity that can be derived from reading comments by people determined to prove how much smarter than you they are. I have one that's absolutely hysterical. I should frame it.