I don't think I've used the word once since high school. Had it been generally unacceptable back then, I wouldn't have done so. I graduated high school in 2004, and it was at least an acceptable insult back then (though not to call a disabled person), I think. I was a jackass in high school, though, so I could be wrong.
Either way, it offends people now, so we shouldn't say it. It's that simple. Deliberately offending people just makes you an asshole.