Brainwashing isn't so much an IQ thing as finding the right angle. Everyone is susceptible to something (flattery, bribery, etc.) and if you use that vulnerability to sneak in the brainwashing it's probably going to be effective.
I took a supervisor prep course in which we had to promise never to use our powers for evil before we could get into personality types and how to "motivate" them. LoL
Garraty's position on brainwashing is spot on. Take the Left, for example, all Leftists ideologies appeal to the base Envy that the lower orders of humans feel about those who have more then them.