[Classic] Weak Men Are Superweapons

I. There was an argument on Tumblr which, like so many arguments on Tumblr, was terrible. I will rephrase it just a little to make a point. Alice said something along the lines of "I hate people who frivolously diagnose themselves with autism without knowing anything about the disorder. They should stop thinking they're 'so speshul' and go see a competent doctor." Beth answered something along the lines of "I diagnosed myself with autism, but only after a lot of careful research. I don't have the opportunity to go see a doctor. I think what you're saying is overly strict and hurtful to many people with autism." Alice then proceeded to tell Beth she disagreed, in that special way only Tumblr users can. I believe the word "cunt" was used. I notice two things about the exchange. First, why did Beth take the bait? Alice said she hated people who frivolously self-diagnosed without knowing anything about the disorder. Beth clearly was not such a person. Why didn't she just say "Yes, please continue hating these hypothetical bad people who are not me"? Second, why did Alice take the bait? Why didn't she just say "I think you'll find I wasn't talking about you?"