I disagree. The relevant question is whether the benefit to society is greater or lesser than it could be from other laws. If someone is sued for a few million dollars from a patent troll who does nothing else for society with that patent, net loss. When something is brought to market that wouldn't have been without protection, net gain.
Patent laws at least in the software arena are very plausibly a net loss. The best thing about this metric is that you don't have to sit there and argue about whether "software innovation" is being blocked, which is something that will just involve people defining "blocked" in whatever way it takes to win their point. (Boring!) It's about net loss or gain.