I guess I just don't understand how this wasn't flagged as a concern when the feature was being worked on? How is it possible that Apple's engineering team built a backdoor like this without it raising serious security concerns? And if concerns were raised why was this not adequately pen tested prior to release?

I'm not sure what's worse from a reputational perspective... A company that prides itself on privacy but can't get something as basic as a firewall right, or a company that knows how to write secure software but occasionally puts backdoors in them for intelligence agencies?