There's always that little catch.
I don't know how practical a 5 round max is. Yes, it slows down a criminal, but it also slows down everyone else trying to defend themselves from said criminals. What's worse is when you consider how accurate people are with firearms under stressful situations against a mobile target, i.e. not very. Even police officers, people that undergo considerable firearms and tactical training, on average put less than 20% of their bullets on target in these situations. With only 5 rounds, it's quite possible that a civilian would empty his magazine without actually hitting an assailant, let alone multiple assailants.
I'm not sure they're quite the boogeyman they're made out to be. Ultimately, they're only used in a small fraction of crimes committed. While an AR-15 is much more potent than my pistol, I can conceal my pistol quite easily, which makes it more effective for committing a crime.