Mao, on the other hand, is more of a controversial guy than just plain evil.
Perhaps that depends on one's definition of "evil", but I would beg to differ.
Mao was responsible for tens of millions of deaths. He also left his country an economic and social mess (Cultural Revolution deliberately and viciously pitted the younger generation against the old, Great Leap Forward stripped the country of its ability to produce crops/food and led to terrible starvation, etc).
He also was a pretty creepy guy and the textbook-definition of a "dirty old man". Surrounding himself with young girls and sleeping with them when he was well into his 70s, because he believed that sex with virgins would prolong his life.
And as has been pointed out in this thread: Most of these guys should probably get unique "talents" that, as a player, you would want to avoid having or implementing. Like Mao's "great leap" could cause all your farms to produce 3 or 4 less food each or the Cultural Revolution would destroy a couple of wonders in your city or a random number of cultural buildings.
Back to the original point of this thread: May I suggest that all you guys who'd love to play as Hitler, Mao, Stalin or some other crazy strongman check out Hearts of Iron 4? In that game, those guys' presence is perfectly valid, due to the nature of HoI as a game/concept.
Personally, I've always preferred playing Civ-games with leaders from long ago eras. Starting my civilization in 4000 AD with a 20th century leader like Roosevelt, Churchill or Gandhi always felt a little off to me.
S.