In this analogy the parent poster would not be seeking to improve society, they'd be seeking to end it.
I don't think that's true.
You can eat fast food once in a while and still be very healthy. They're not necessarily advocating for (metaphorically) shutting down all fast food restaurants, just making a point about over-consumption side effects.
At least that's how I read it.
That's how you read it because that's what they said. Not sure why the original reply felt the need to add "stupid" as "So people love it" makes the same point. Mister Gotcha is probably replying implicitly to the addition of 'stupid' to make a point. Except now that they've stuck their stakes in the ground and are getting defensive, let the pedantic internet slap-fight commence