Bruce Schneier nails it: "efficiency is not the most important goal here; security and liberty are."
The world has changed dramatically since the NSA was founded 62 years ago. Back then, it was easy to spy on foreign governments while shielding our own from snoops. Today, the NSA's intelligence mission has expanded from just government-on-government espionage to government-on-population surveillance. At the same time, the communications world has shifted from dedicated circuits that can be passively tapped to a single global Internet infrastructure that requires active attack to eavesdrop on. Everyone uses the same networks, and creating the capability to eavesdrop on foreign communications by engineering backdoors into US technology leaves domestic transmissions vulnerable to eavesdropping. The NSA's aggressive data-gathering, with seemingly little regard for how that might compromise the security of everyday digital communications—and with only loose oversight (at best) by government watchdogs—has far exceeded what any modern and free society should reasonably expect. Breaking up the agency would do a lot to bring it under control.
How to Save the Net: Break Up the NSA [Bruce Schneier/Wired]