We all hate patent trolls so much because there's no way to know whose patents we're violating before we get sued. But there are also cases where, whether or not we approve of the patent, everyone at least knows it exists. Like Apple patenting magnetic laptop chargers. Everyone knows that if you start selling a MagSafe competitor, Apple is going to sue you.

So one of the problems you have to solve if you create a NATO-like network of companies, is that one of your members might decide they want to go up against Apple. Now your organization has to decide what counts as a "troll" case and what counts as "you should've known". And since some industries are at a higher risk of trolling than others, those more expensive members will inevitably drive out the safer members who foot the bills but don't benefit very much.

So in the end you have problems somewhere in between an insurance company and...NATO :p