Re: teaching the blind
Nicely put Jon. I suppose you have to look at the specific circumstances. Why the person wants to train, and if it's plausible to do so in that particular dojo.
I also don't like the idea of saying "You're blind, you can't do this!" But perhaps it would be prudent to simply direct their focus onto something more suitable to their condition.
I recall taking gymnastics in school, but once I exceeded 6'3", the coach was like "You should probably try volleyball instead of this." Which I did. But it wasn't him crushing my dreams of being a gymnast, rather he was simply pointing out an obvious issue and a giving me a legitimate alternative. I ended up being happier playing volleyball, btw.