Threatens liberty, doesn't threaten the bad guys.
It's one thing for common carriers to be required to allow tapping into their own networks for law-enforcement purposes, quite another to dictate what individual parties can and cannot do with their own communications.
Does anyone think for a moment that serious crims are going to be impeded by this? Maybe some penny-ante sorts whose crimes don't amount to much and who can't be bothered doing their homework will be bothered if Skype has a back door, but that's about all.
Leakproof encryption tools will not go away, and anyone with even a hint of determination will find them.
Then there are open-source communication applications, from Thunderbird to Pidgin. The only way to to back-door them is to ban them outright. How far do you think that idea would fly? All of them by nature have the capacity for encryption, if not in a current implementation (like Enigmail for Mozilla), then potentially.
When encryption is outlawed, only outlaws will use encryption.