That's not true at all. It's those who made up their minds to be good but aren't who do the most evil.
I'm not sure that's true in aggregate. I think most of the evil is done by people going along with things - like, if you talked to them about it for a while they'd concede that some aspects of what they were going along with were sort of questionable and maybe a bit bad, but they don't think about that spontaneously.
Here's another installment of rationality quotes. The usual rules apply: