Maybe being blunt and calling them what they are is more prone to succeed, nothing else did, not even when it's so abundantly obvious.

It's the equivalent to a good slap to the face when trying to make someone come to their senses.

At the end of the day everyone is responsible for themselves, if someone has decided to close of their God given gifts of logic and reflective thinking then no amount of pleasantly trying to explain would do anything, you can talk until you're blue on the face, they'll keep being retards if they want.