Additional concept - At least half the reason that negotiations didn't work out was because the Quincies were perfectly aware of what the Gotei was. They were, quite naturally, somewhat reluctant to leave the defence of their homes and loved ones in the hands of a bunch of psychotic monsters when they had the capability to do something about it.

Hell, if they connected the formation of Hollows to the concept of ghosts who were basically devoured by their own fear and anger, the logical response on the part of the Quincies would have been to do all they could to make sure people died happy, and that ghosts found a measure of personal peace and contentment through learning to let go rather than simply being hit with a konso (because I'm fairly sure not everyone becomes a ghost on death, and not every ghost requires a Konso - it's just the most efficient way to do it).

So, original Quincies? Totally good guys. New Quincies, not so much.