Lots of people are stupid and telling so just makes them more insecure and more dependent on their fantasy world.
If you honestly feel that way, why even think about what they say? Ignore them. Pretend they don't exist and, maybe, they'll leave you and everybody else alone?
Isn't that what religious zealots usually do when you decline to engage them? They just shut up and stop trying to control everybody else's life when you ignore them, right?