Of course, there will be, as Justice Stevens predicts, an "avalanche" of legal challenges to gun laws in the wake of McDonald, some by the gun lobby, but most by criminal defendants seeking to overturn indictments and convictions for violating those laws.
Now who would those criminal defendants be? This is one of those moments where language is everything and sadly, the gun controllers have defined the language.
Most people when they hear the word "criminal" think of gang members, bank robbers, murderers, thieves, etc. Essentially, people who have committed crimes against person or property. So when the uninitiated hear Dennis Henigan speak of criminals using the McDonald ruling to overturn indictments and convictions, they're going to think, "OMG! This is going to put horrible people back on the streets and they're going to have guns! ZOMG!"
And don't think for a moment that this reaction isn't what the Brady Campaign wants. Gun controllers have never been above using carefully-crafted, intentionally vague language to confuse and alarm the masses into supporting their agenda. "Assault Weapons" and the "Terror Gap" being two examples.
So who are the criminals that Dennis Henigan speaks of? The criminals are people like this and people like this; People who are only criminals because they dared to defy the draconian legislation prohibiting anyone from owning a handgun. Draconian legislation that he has helped create and defend to the bitter end.
Now that you know what a "criminal defendant" really is do you see the reason for Dennis Henigan's concern? I personally hope that his concern is valid and that the "criminals" that he and his movement helped create will finally get justice at the feet of the McDonald ruling.