It seems to me like the main reason that playing as Taliban is controversial and playing as Nazis isn't, is this: WW2 is in the past, while the Afghan conflict is contemporary(well, yes, duh). The big-bad politicians think it's disrespectful to the soldiers.
But then you'd think that playing as nazis would be disrespecful to those who fought in WW2, right?
Hell no, that's in the past, not that many that cares enough to take offense.
I guess it's sort of obvious, but lots of people here are complaining how this isn't OK but playing as a Nazi is. As why most of the other Modern warfare-games slipped by unnoticed, maybe it's because this one actually blatantly says "Hi, we're the Taliban! Will you come and play?".
But yeah, it's all a game, aside from being interactable(although that might be why this is a problem, too), it's just like any other form of medium.