The harm is straightforward -- the lost patent licensing fees the infringer would have had to pay to use the patented invention. An inventor who has no money to take his invention to market licensing it to someone that does is part of how the patent system is supposed to work, so the fact that trolls also don't take their own inventions to market isn't anomalous in that regard.
There can't lost sales unless you were also selling the patented item.
Not even if it occurred during the lag time of you bringing it to market. (If this ever actually happened without corporate spying and intentional infringement, than the patent was clearly too obvious)
Lost sales aren't the only form of harm. Imagine you bought patent rights for 9000 dollars from original inventor, counting on this patent be very useful and you benefitting greatly. Now everybody uses it, but you are not paid. You are obviously harmed - you're out of $9000 and got nothing in return. Roughly the same situation as you buying a rental apartment and people living there not paying the rent (at least within the current framework of treating patents as property rights). Clearly you have a standing here.
This is the comment thread of an article about how non-practicing entities now make up the majority of patent infringement cases in court. You're asserting that every single one of them is represented by a law firm which is making up a nonexistent class of damages, and every judge who has awarded damages to a non-praticing entity in the past made a mistake in doing so.
That's not right, obviously. Title 35 of the United States Code states that "the court shall award the claimant damages adequate to compensate for the infringement, but in no event less than a reasonable royalty for the use made of the invention by the infringer". Thus the basis of the damages is unpaid royalties for licensing the patent, not lost sales. The court may award damages for lost sales or anything else it considers "adequate to compensate for the infringement", but the ONE statutory-defined harm is the one you're saying doesn't exist.
