I really like her. Especially on days when I'm feeling particularly clumsy myself.
I think she may be a lot smarter than most others will give her credit for.
A few points:
-Having crossed eyes does NOT necessarily equal being mentally disabled.
-Being clumsy does NOT necessarily equal being mentally disabled.
And--even if she were, so what? Why does that constitute an "insult" to mentally disabled people? If anything, it would be a sign of inclusion.
Okay, so Rainbow Dash was impatient with her in that scene from "The Last Roundup." That's just Dash being Dash. The alteration of Derpy's voice and the deletion of her name (just iTunes version, thankfully) was MORE insulting. It implies that if someone's a little different, they have to be changed so they will be "acceptable." (Any FUTURAMA fans reading this: I refer you to "The Cyber House Rules" for another example.)
A side note for those of you familiar with the 1980s MY LITTLE PONY: Derpy reminds me a bit of Fizzy the unicorn (as I recall, she was a bit clumsy herself, and no one had a problem with that). Considering that her (fanon-only) daughter is a unicorn--maybe they could be related? (Similar cutie marks, too.)
I hope Derpy gets more screen time, with her original voice and eyes. There is such a thing as being TOO "politically correct."
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The existence of the leader who is wise
is barely known to those he leads.
He acts without unnecessary speech,
so that the people say,
'It happened of its own accord.' -Tao Te Ching, Verse 17