So what would be the point of getting permissions for mods in the first place if they're going to break one of the most important rules? In my opinion that's the same as stealing.
You wouldn't steal a car...
You wouldn't steal a baby...
You wouldn't shoot a policeman...
And then steal his helmet...
Then take a dump in his helmet...
And send it to his grieving widow...
And then steal it again!
No, wait, that's downloading movies illegally.
In any case, donations ain't stealing. First off, it's voluntary. If it isn't it's robbery, not stealing. You get zero extra features usually for donating unless you like pretty thingies like capes or hats, and in some cases, it's a option to test the bleeding edge version of a mod with all the "FUN" that entails. Or the slight advantage to download from a different source, maybe ahead of time, maybe with better bandwidth. Features locked away until you buy them? Not likely, but also not that hard to do either. No real benefit in Minecraft, though, unless Mojang did it. They had a good april fools joke with that idea. I quite enjoyed it.