The problem was that it was made useless. If you ask random people to teach your chatbot, you are at the mercy of those random people. Sure, MS could have left

The problem was that it was made useless. If you ask random people to teach your chatbot, you are at the mercy of those random people. Sure, MS could have left it on, and no one would use it except for two groups: actual neoNazis, and people who think a Nazi chatbot is funny. The mistake MS made was they forgot that people suck, or, at least, enough people suck that what they did was a bad idea.