The original purpose of patents is to entice technological innovation. By giving inventors exclusive rights to their own inventions for some amount of time, this entices people to invent, develop and improve on new ideas and new technologies. After all, money is often a very good incentive.
This original intent becomes more muddled when a patent owner can transfer this ownership to another person or company. Sure, the original owner (usually) gets money for it, which is the point... but now that other person or company is making money from an invention they did not develop.
It's still in the realm of acceptability when the intent of that patent buyer is to improve on the invention. After all, it makes sense. A lone inventor might not have the resources (or motivation) to improve further on the invention, so if a richer person or company wants to improve on it, that's only beneficial overall. The result is further technological progress. Even though the patent was transferred, the new owner contributes to the overall progress.
But what happens if a company is based exclusively on making money by buying patents and then enforcing them (ie. demanding license fees and suing people for patent infringement), with zero contribution and zero improvement on those inventions?
These are so-called patent trolls. That's their entire form of business. They do not contribute. They only leech money, and nothing else. The original inventors do not get any of this money, nor does the money go into further development. All of the money simply goes to the pockets of the patent trolls. This is purely opportunistic behavior.
Recent statistics show that in the United States over 60% of all patent infringement lawsuits are made by patent troll companies. The problem has really gotten out of hand. (And the vast majority of these cases are settled out of court. This is actually a deliberate tactic by the patent trolls. If the case went to the court, and it ruled against the patent owners, this would nullify the entire patent. By settling out of court, the patent trolls never put their patents in danger.)
And, naturally, the license demands and lawsuits are often astonishingly egregious. Because patents, especially software patents, are often very vaguely worded, they can be applied to a wide variety of applications.
There are countless stories of people getting surprise demands of license fees or lawsuits for things they didn't even know was patented, often because they are extremely trivial things (even though trivial things shouldn't be patentable, even in the United States). In some cases the thing they are using was invented way before the patent was filed (sometimes even decades before).
Patent trolls are opportunistic leeches who only suck money out of people without any kind of contribution to progress. They often also sue people for things that would never hold in court, and bully the person to either pay licensing fees or settle out of court, and thus the validity of their patents are never tested.
Curiously, this tactic seems to work both against individual people, and even megacorporations, which is rather amazing. Megacorporations would have the money and the army of lawyers to contest the patent claim... yet still it seems that many of them choose to pay instead. Sure, to a megacorporation the sum they have to pay is minuscule relative to their revenue (and perhaps that's the reason they simply choose to pay), but one would think that a megacorporation would be above getting bullied by a troll. But seemingly not.