I don't think it's possible to have a retroactive tax on instances of patent trolling, as opposed to patents in general. In order for this to be a tax and not a

I don't think it's possible to have a retroactive tax on instances of patent trolling, as opposed to patents in general. In order for this to be a tax and not a fine, it seems like it would need to be a tax on the patent application, not on bringing and losing a patent lawsuit. And in order to determine at the point of application whether or not a patent will be used for trolling (which we might define as whether the patent will be used in a lawsuit by an entity that holds the patent but does not itself employ the patent's "invention"), the USPTO would need to be able to read the future.