Well as others have pointed out, it's one thing to deliberately engineer a backdoor, its another to find an exploit in an existing system and then use it to stop a scumbag from hurting people. One is a total violation of someone's privacy and expectation, another is simply good ol police work.

So I'm happy with this outcome and even not opposed to the procedure, but I'm very much against deliberately engineering backdoors in systems. I think that position is pretty consistent and sound.