I'm not sure I see the ethics argument re: how the limitations affect your ability to back up / consume / multi-device. Those things might make it not worth your time and money, they might make it a bad deal, but it's not unethical to accept a bad deal.

For me, the ethical dimension comes from how the DRM will be abused. By paying somebody who develops DRM, you're complicit in building something that may later pivot from protecting content to silencing dissent or preventing local-manual override in a hazardous way, and that's unethical. Maybe it's not right up there with biological weapons, but it's still one of those things that we should not tolerate.