Besides that, the crime rate has been falling during a period coincident with aggressive policing, more incarceration, and more legal measures (RICO) to fight organized crime. While people have alternative theories for that decrease (e.g. banning leaded gasoline), aggressive policing cannot be ruled out as a reason for the decrease in crime.
Finally, tape recordings and wire taps are the backbone of investigations of sophisticated crime. It's disingenuous to pretend that pervasive encrypted communications doesn't dramatically change the landscape law enforcement is dealing with.
I happen to think the privacy benefits of encryption outweigh the cost to law enforcement, but I think it's ridiculous to pretend like there isn't real crime out there or that encryption doesn't make it harder to fight it.