Kait- as froggie points out, "stupid" is a perfectly good word to define some actions and states of being. The trouble with promoting a politically correct lexicon is that it's not the words that are the problem, but the attitudes behind them, when they are used to hurt those who don't deserve being hurt. As you might probably guess, neither froggie nor I, nor probably any other smrtie, is going to use the word "stupid" (or "derp", or "crip", or whatever) to make fun of the handicapped. But I have no compunction against using these words in appropriate contexts: for instance, in making fun of someone like Ray Comfort, who is willfully ignorant and fleeces the even more ignorant for his personal profit. Much of what he says is stupid, and he's willfully stupid to say it, and I don't see what's wrong with saying so.
Steven Pinker points out (in, I think,
The Language Instinct) that when a word becomes derogatory and is shot down by the political correctness folks, all that happens is that the new, "nice", term eventually also becomes derogatory and is in turn shot down, which leads to what he calls the "euphemism treadmill". His example is the progression from "black", to "Negro", to "Afro-American", to "black" again, etc. The same is true of the series "crippled", "disabled", "handicapped", "otherly abled", etc. The problem is not the words themselves, but the
attitude: as long as there's racism, or ableism, or whatever other -ism, the negative attitude will glom onto the current word and eventually make it derogatory. So trying to police the language is a vain attack on the symptom, not on the disease, and won't help anyone.

You were born. And so you're free. So happy birthday.
- Laurie Anderson