The "Everybody should be armed" narrative is spread by people who can't even properly justify their reasoning. They always throw a "they should have been armed and they wouldn't die" or something as dumb "all school staff should be armed". I learned to ignore them and their wild west fantasies.
Good idea. I've found the best way to engage (if you want to engage) is to just take the argument seriously, and ask what kind of society they envision, in detail. It gets awkward quickly.