Honestly, it depends on the campaign setting. In the Forgotten Realms, Drizzt has softened the feelings towards dark elves, whereas in Greyhawk, drow are pretty much universally regarded as evil, and they simply do not exist at all in my homebrew setting. Can you play a warforged not in Eberron? Sure, if the GM allows it, but they will be out of place, regarded as a curiosity at best, and some kind of golem at worst. If it's just that I, personally, hate bards (as an example), that's not a good reason to exclude them. But, if I'm running a setting where all bards are arrested on sight, then the players probably should be encouraged not to or restricted from playing one (or at least made aware of the risks of such).