So after thinking about it a bit, I'm going to jump in and defend the mouse. Just a little.
it is true the Desert Parties sell out, and fast. Whether they are are good value or not, they sell out and it's hard to get reservations for them even at 180 days (or however long out you can get them). So there's a demand. And it seems reasonable for Disney, if there is an unmet demand, to try to cater to that demand.
What we're basically arguing here is that Disney should deny people the chance to pay for something they want, so people who have already established they do not want to pay have no negative consequence. That's like saying a restaurant that has patio seating should allow people who are not eating there to take up al their tables -- heck, why don't they just let everyone into CP for the character parade. Or let everyone in BOG to meet the Beast and look around. They've established that certain experiences at the park cost more, and we all sign up with that understanding in mind. So maybe this isn't the money grab as much as it is about letting some people buy something they want.