There would be no reason to buy the license because you'd lose in court if you weren't using it. Companies could just use it with no fear of you winning a case

There would be no reason to buy the license because you'd lose in court if you weren't using it. Companies could just use it with no fear of you winning a case against them. You can't even just accept that the originating patent holder should be able to sue while anyone who buys the patent can't. Patent trolls would just hire the person who registered the patent or sue on their behalf. There is no elegant solution to the patent troll problem. If someone can sue, then trolls can sue.