If that were so, then the universe wouldn't have designed our species to requisite one half (males) to mate specifically with the other half (females) in order to continue. Instead, it would have made it possible for each and every human to do each and every task to an equal capacity to all others. Some can't walk, some can't hear, this alone as well as the gender factor prove that the universe intended us to be categorized physically. As for mental categorization, that's perhaps the only plain on which you can argue that case but if you truly would force a mentally or socially challenged individual with either Down's syndrome or autism to perform at their full potential in mainstream schooling, you are not just screwing up your kid's childhood but you're plain ignorant to a person's needs that you're supposed to love.