Regulation of cryptography can help investigations but regulation is still a bad idea. A good explanation is something that my ethics professor said. It was something along the lines of "If a pen was used to write orders for the army to start WW2, should pens be banned?". The war would probably happened anyway even if pens were banned/regulated and it is certainly not the cause of the war. Cryptography is very similar: even if it would have been regulated, criminality will not just vanish.