"The onslaught of litigation brought by 'patent trolls'..."

"... who typically buy up a slew of patents, then sue anyone and everyone who might be using or selling the claimed inventions — has slowed the development of new products, increased costs for businesses and consumers, and clogged our judicial system...."

Because they don’t manufacture products, they need not fear a counterclaim for infringing some other patent. They need not be concerned with reputation in the marketplace or with their employees being distracted from business, since litigation is their business.

AND: Here's an excellent episode of "This American Life" about patent "trolls":