higher intelligence will serve only to come up with better arguments to defend a wrong position - Waton
I also found that very interesting. It's so important that we have the courage to face challenges to our beliefs with honesty.
Having said all of the above, I still believe that presenting evidence to people with strongly entrenched ideas can pay dividends in the long-run. However there is usually some crisis of faith before the things they heard previously become significant. It might be a change in doctrine or a personal grievance.
In my own case it was facts that convinced me to leave but it was the dishonesty and arrogance of the GB regarding the 'generation' that prompted me to investigate.