I don't agree running around stealing add-ons from people known to actively contribute to the game, and to release their things. The fine line would be if they just didnt' release their things, but actively did stuff.
But if you know the creator is on the verge of running away with a metaphorical 'million-dollar' worth add-on, or even a couple, just for their own selfish or unknown reason, then why the hell not?