It is an accepted tenet of the State Dept that if a Green Card holder wouldn't have have passed an admissibility test due to actions at or prior to the time of his request (sorry that's so convoluted. I flunked writing), he is subject to deportation if he commits those infractions while in the US.
A person who led protests and riots (yes, they were) in another Country and applied for a passport to the US, would be denied.
So if a person comes here on a Visa, gets a Green Card and his actions are of the sort that would have prevented him from getting a Visa in the first place, he can be deported.
The Court, in this case, is just dotting the I's and crossing the T's. Meanwhile, he's cooling his heels somewhere. Probably Louisiana.