Encryption is the only way to secure information. This is true for criminals and non-criminals alike. To deny encryption is to deny security to everyone.
Presuming it's the criminals who will look to exploit these vulnerabilities, denying security is making every non-criminal susceptible to attack.
So the only question that needs to be answered is this. Do we want to protect our citizens? The only answer is yes. The only solution is encryption.
The problem with strong encryption is that it already exists. Even if strong encryption were made illegal, criminals will be the one's securing their data despite the law. To deny citizens the right to protect themselves is just putting them all at risk. It's disarmament.
Under the law, all the police should need is a warrant. It's not even an exception to any rule.