On the web, it is sometimes hard to speak without sounding all hot under the collar.......this isn't meant to sound angry, so don't take it that way. I just have a few comments and some questions for those who make multiple ADR's.
One............. Yes, it is rude and yes, everyone knows it.

So, when you are at home, do you make three dinner reservations and only show up for one without cancelling the other two? Just wondering.
Two............. Disney doesn't even need to go as far as a CC hold. When someone goes to make a reservation within two hours of the other one, they should have a policy that the CM will not take the reservation. I would have no problem with that. I don't need to eat a sit down meal every two hours.
Three.............. so you all that make multiple ressies........you are telling me you don't know a few hours ahead of time where you will be eating so you could cancel the other one or two ressies? I must be too good of a planner........I know WAY ahead of time where we will be. And if I don't, I would just choose my counter service meal then.
Seems easy enough to me.