Jesus, Satoshi, you're the king of double standards, aren't you? Muchul didn't have any objections about going with the Rockets, and no matter what those overprotective Rougela felt about it, people "catching" wild pokemon the same damn way he has done before is something he could stay out of for once. Catching wild pokemon is what people do in this world.
The Rougela were in the wrong by attacking a nearby city because their fellow pokemon willingly went with a couple of trainers who didn't even know of the Rougela sisters' existense. Stopping the three pokemon would be the right thing to do, not trying to get Mucul back. Again, catching pokemon is what people do in this world, and it's not like the Rockets were doing it by unethical means this time. They simply stumbled upon a pokemon they wanted, and the pokemon didn't have any objections going with them. We've seen a lot of pokemon being caught in the exact same fashion during the show.