Diablo 3 does not have a single player mode. It has multiplayer with a private game option. Whether you agree with the design choice or not, that's what Blizzard went with.

The "entitled gamer" thing comes form people thinking that they can tell a developer how to create their own game. It's not the same as gamers expecting companies to make good on promises (ala with the ME3 endings).

Supporting offline single player isn't just a matter of turning off some sort of DRM, it's a matter of redesigning the game fundamentally from the ground up to be played client-side. It's an extra feature, and it's one that Blizzard didn't think it was worth implementing (I tend to agree, but that's besides the point.)

The best D3 experience, according to Blizzard, and I think according to the vast majority of fans, is when you have access to the Battlenet community. It's how anyone serious about D2 played that game, and it's how Blizzard designed D3 to be played. Again, you can disagree, but I think people who really would utilize the offline single player are a vocal minority, and Blizzard obviously didn't see fit to include this legacy feature. I don't blame them.

The launch was rocky, but the service has only gotten better since, and a few months from now no one will remember that the servers were unstable on launch day. People got a multiplayer game with a rocky launch, which is regrettable, but not entirely surprising.

I fully understand people complaining about the servers, but what I don't understand is people complaining about a game which has been marketed as multiplayer only not having an option to play offline. Again, it's like buying World of Warcraft and complaining that you can't play on your own private server.