This should be obvious to everyone here, but it's pretty much inevitable that if a backdoor exists, criminals will eventually find their way through it. Not to mention the "legitimate" access by corrupt and oppressive governments that can put people in mortal danger for daring to disagree.
No doubt that is true, and presumably Cory Doctorow has written some article making that seem like the only concern. The alternative makes it difficult to enforce all kinds of laws, though.
