Patent trolls are Non Practicing Entities who file lawsuits against companies who are actually practicing an invention. The problem though is that when the United States was created, it chose to drop the requirement to practice for a very specific reason: it discriminates against the poor and middle class, who might be smart enough to invent some world changing technology but have no way to raise millions of dollars to produce their invention. Such a requirement was seen as anti-democratic by the founding fathers, and historically NPEs have actually made huge contributions to human knowledge... E.g. the person who invented the computer didn't have the money to actually go out and build one.
There certainly have come to be a lot of abuses with the current system that need to fixed. But it's worth keeping in mind that while Mark Cuban himself might not be a bad guy, the reason the founding fathers chose to let people file patents without having to build out the invention was precisely to protect us from people like him, who could come in and just steal someone else's efforts wholesale because they happen to have more money. And in the past couple years, a lot of law professors who were originally against NPEs have now reversed their opinions and acknowledged that the situation is more complex than they had originally believed.