Applying for a patent is a costly and tedious process, so it's not strange the there are companies ready to take the work from individual inventor's hands. If that weren't allowed, large companies would have an advantage since they have a legal department. In any case, making a law against patent trolls would be difficult because if you require a minimum amount of non-patent work from them, they would simply meet that amount and keep on trolling. I think the solution is not to make rules against them specifically, but to change the incentives. First make sure patent applications are non-trivial. Second place the initial burden of evidence on the plaintiff to prove that their patent is actually being infringed.

But you're right, these people have no shame. But it's just not the patent troll, it's also a host of lawyers and judges who have interest in this stuff going on.