If a blind woman was grabbed, dragged into an alley and being raped, would you hope she had a loaded derringer in her pocket?
That's the gray area right there. In fact, the respected firearms expert Massad Ayoob has argued for giving firearms training to the totally blind. He uses an argument much like yours.
For me, it's a tough call. All I can say is this. If the woman were my wife, and she had any sight, I'd want her to be carrying a firearm.
But if she had no sight at all, I think a contact stun gun would be the way to go. Not only would it be safer for innocent bystanders, it would also be more practical.
But I'm still uncomfortable with that. You shouldn't be basing rights on practicality. But common sense must play a part too.