If there were a way to magically ensure that only the good guys had access to the information, I'd be way less concerned about these measures. (There are only a few things that I care about being secret for the sake of secrecy, and I can easily keep those off of computers.)
Every encryption backdoor is a huge vulnerability. Even if we somehow ensure that the powers-that-be remain entirely trustworthy (something that, historically, we can't even manage for a century), they're not the only people who'll have access to the backdoor. It's not possible to make an encryption backdoor that only authorised parties can use: as they say, the laws of mathematics do not respect the laws of Australia.
