I totally empathize with you, OP, but don't quit the game. At the very most, quit the guild.

I myself am legally blind, but I can still see well enough to function in most cases. There are times though in the game when visual cues are too subtle for me to pick up on, and I or my team suffers greatly. Most of the time they're cool, but there are days when no one feels like getting on mumble to call stuff out and it's discouraging.

Don't quit the game, but if you feel you need a break from raiding, go for it. You gotta do what makes you happy.