I think this is true, however how do you get one? Most dictators are not benevolent. Lots of times they start out benevolent and end up not.
Have you ever seen the image of a woman who is past the point of pulling her hair out from her children's incessant "mommy I want that", "mommy he touched me!", "mommy that's not fair", etc. etc. etc.?
Now imagine you are that benevolent dictator (Mommy) and you have several million subjects (children). Kinda makes your skin crawl...
Add to that the adage Power corrupts and absolute power corrupts absolutely and it's not so hard to see why good men go bad.