Mere assertions that they "should be perfectly capable" are just vacuous statements that don't mean anything.
1) We're not just talking about the US government that will have access to keys.
2) The US government has shown itself to be perfectly capable of losing secrets. I'm not saying, as you did, they "should be." I'm saying they have proved it. So have the governments of other countries.
3) We don't know how those countries got all the information they have. We may know where some of their information came from, but not all of it.
4) NSA is supposed to be our best and brightest at protecting secrets. Look what they did.
5) Some proposals for encryption backdoors allow for access by law enforcement at almost any level, down to local sheriff / police. They would probably stop just above mall cop, if they could.
If you have a retort to just some of these points, unfortunately that doesn't fix the problem. You would have to be able to answer all of them. A leak only takes one weak point.
