Statistically, some nonzero percentage of people with a gun are nutjob cop killers. That's the end of the argument right there. There's nothing else to be done because cops aren't trained to gamble on the situation (and keep in mind that cops are dealing with a large sample size, though these look like isolated incidents to us). It's super weird to me that this isn't obvious to people. Maybe armchair theorizing about situations involving guns simply has too much allure.