@ziggurat I certainly agree that specific events can be ignored or what-have-you. But in terms of wide-spread social wobbling, I think it'd be... disingenuous, I guess, to totally pretend they're not there.
I'm not saying that every plot or NPC or whatever has to react to it outwardly, but the perception and feeling of a time and place should be preserved as much as possible. Naturally, if you're setting a game in now, and an event happens you aren't prepared for, then skirting around it is definitely appropriate especially if it's of a horrific nature.
I'm also not shouting for PCs to react 'authentically' really, though that's an option if that's what you want to explore... There are ways of portraying a level of racism or sexism or homophobia without outright yelling 'bender' every opportunity you get.
Still, games are about fun and if something isn't fun to play, you shouldn't have to play it. That said, if you don't find it fun to explore the causes of, say, the Harlem Renaissance, then you shouldn't use that as your backdrop. If you don't want to explore the legend of the Trojan War, don't set your game in the period that's going on.
Most folks don't play a modern game to explore those themes, and that's fine. But if someone says "oh we're making a game set in the latter half of WWII in California..." some folks are going to think "Okay... so are the Japanese-Americans in camps, or..."