An additional point that hasn't been brought up yet is that Civilization games are not meant to be historically accurate: they use history as inspiration for their systems, nothing more. We kid ourselves when we say we're playing as Bismarck or Washington or Napoleon in Civilization. instead, we're playing a civilization that follows a custom ruleset inspired by those leaders. It's sort of similar to how weapons in military FPS's have the names of real weapons: the weapons you're playing in-game are simply inspired by those real weapons and aren't (in most cases) meant to be anything more.
The reason I bring this up is because even if a mod includes a leader/civ you find offensive, remember that what they are actually doing is using that leader/civ as inspiration for an "abstract", possibly even caricature, leader/civilization that they actually implement with their mod. If you choose not to play a leader/civ solely because you find them offensive, you are doing yourself a disservice: if the modder created something truly unique, you are worse off for not willing to experience their interesting creation solely because you find their inspiration offensive.
A prime example would be that UA mechanic brought up by JFD earlier in this thread: if it were attached to a civ that you found offensive, you would never be able to actually experience that UA mechanic. The more sensitive you are to this kind of stuff, the more of these types of experiences you might miss out on.
Or, let's say I'd make a UA inspired by 20th century dictators: workers can be sacrificed to instantly finish the improvement they are building or to add hammers to the current production of the city they are stationed in ("Forced Labor"). Granted, it's probably terrible, but there are a variety of neat things that this UA could cause, especially in the earlygame on Marathon Speed. Would you really want to miss out on messing around with this mechanic simply because I gave it to a civ/leader that served as its inspiration (pretty much all 20th century dictators would do)?