Well, seething is never a useful or positive state of mind. Blind people or others with medical equipment or bassinets or whatever need to travel as much as any of we able-bodied, and the best response would be to accept that the good seat has been given to someone with a better need.
I think we've all been there, where our carefully-selected seat, after research in Expertflyer and Seatguru, has been swapped or vanished in an equipment change or some other calamity. I remember my Y+ seat on one of the last QF flights out of SFO turning into Y. Four of us had enjoyed the wide seats on the way over, but when it was me going home alone, it was a different configuration, and the big seat had turned into a small one.
I sucked it up and squeezed in.
A blind person traveling with a dog, or a baby in a bassinet or whatever, really needs to work out seats ahead of time. The computer seating algorithmn doesn't necessarily know their specific needs, and turning up at the last moment expecting that someone is going to be turfed out and a good seat made available is a bit rich. That someone could have been another blind person with a dog who had thoughtfully prebooked. They could set their dogs on one another, I guess, and wouldn't that liven boarding up!
Nowadays, with paid seat selection and exit rows for a surcharge, there may be an actual loss of money or points if we don't get the seat we paid for. And of course, if one suspects that someone is sitting in your seat who really shouldn't be, then a FA could be called to sort out who should be where. Meek or not, it is a blessing on the FA to help, to be the angel of righteousness and possibly wield the enforcement devices I always expect they keep in a special locker.
