I agree that 'don't feed the trolls' is an untested folk theory that we shouldn't necessarily assume works, but your argument seems to assume that the expected result of not feeding trolls is no trolls at all, which I'm fairly sure is a strawman. The point of not feeding the trolls is, as far as I can tell, to minimize how disruptive they are when they appear. It's more analogous to "if you cut yourself, apply first aid and consider seeing a doctor" than "if you want to avoid scurvy, make sure to get some vitamin C in your diet".