>Using the patent to to produce and sell the invention, in which case it's not a paper patent.
If they're successful, patent trolls end up with licensees too.
If you're not allowed to sue anyone until you already have licensees, then if you invent and patent something and pitch it to a company, you can't sue them if they rip off the idea.
Either a) Using the patent to to produce and sell the invention, in which case it's not a paper patent.
Or b) Using the patent purely to sue other people (which is what most of the big name patent trolls do) and therefore must be stopped.