But you can't. If you are a large corporation, the only thing determining whether an opponent is a patent troll is whether you can dig up a patent of your own

But you can't. If you are a large corporation, the only thing determining whether an opponent is a patent troll is whether you can dig up a patent of your own that the opponent is violating. If you can, you can use the mutual threat to enter a patent sharing agreement. If you have no way to threaten the opponent, they must be a troll. To them, there is no effective difference between a company that only files patent lawsuits and a startup that has been forced out of the market by competitors that are violating its patents.