Where would dictators be without our compliant amnesia? Make the collective lose its memory, you can conceal… — Charles Stross

In my experience, the best way to deal with such people is to politely agree with everything they say, then ignore them.

If I forget, then it might as well never have happened. Memory is liberty.

You know, if I tried to change the minds of everyone who I thought needed changing, I’d never have time to do anything else.