They went after a soft target. If disability is being specifically targeted, it's only because disabled people are de facto a soft target.
The ones you need to worry about hate and persecution from aren't the looneys with guns. They hate you, but not because of disability in particular. They hate you because you're not under their thumb. Because you're a woman in pants, a man without a beard, not an ultraconservative Muslim (Christian, Jew, etc.).
The ones you need to worry about disability-based discrimination from, unfortunately, is society in general. Until it became CLEAR that this was an act of Islamic Dominionist terrorism, CNN et al were trying very, very hard to frame it up as another mentally ill/developmentally disabled shooter. What that tells me is that it's more socially acceptable to "blame the 'tards and crazies" than to consider blaming those who have an avowed mission to destroy everyone who doesn't see the world their way.
THAT scares the crap out of me.
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"