I've had conversations with disability rights advocates who are concerned that any form of voluntary assisted death will quickly turn involuntary once the legal shackles are struck off "caregivers" who are entrusted with the welfare of people who require complex, expensive care. There's certainly a precedent for that. However, there's also clearly a precedent for removing the agency of people with disabilities based on the assumption that they're all big infants who can't be trusted to make responsible life-and-death decisions for themselves.
That puts us in a position of being too expensive and troublesome to live, but too crazy and dim-witted to die. Or at least too crazy and dim for the kind of "soft" death we prefer for our pets. Violent, lonely, and needlessly early death is apparently okay for humans. (I.e., if you can no longer blow your own brains out, you've waited too long. So shoot yourself now, while you can still act unassisted!)
I've never met a VAD opponent who actually said, "You know, I'm too much of a loony and an idiot to decide that I want to live." It's always someone else (me, specifically) who is too much of a loony and an idiot to decide they want to die. I don't think that presumed incompetence helps safeguard anyone's rights, though.
As dangerous as it is to grant J. Random Disabled Person the power of life and death over his/her own body, it's more dangerous not to. That's when you stumble into the arena of protecting the poor little cripples from themselves, and no good comes from that.