Data was artificial and autonomous. The Dr originally wasn’t autonomous, it could be argued he’s just part of the ship, but the holo emitter changed that. I’m amazed the Daystrom institute let him keep it, but since it’s apparently his, and that makes him autonomous, I would argue he’s just like Data (minus the permanent corporeality of course). I suppose there’s a question about ownership given his origins as a Starfleet asset, but since he can be replaced with a copy of the original program, there’s no real material loss in letting him leave the ship.
Tacos.