TSA locks, anyone?
Since when to travel to USA you are forced to ensure your luggage carries a standard backdoor - of course just to be used by TSA personnel for security reasons - your luggage can be easily opened by anyone, and if you really store anything valuable in it, you're really very naïve or an idiot. I would like to know how many terrorists have been arrested or deterred by TSA locks, and how many goods were even more easily stolen because of them. And often, by TSA personnel itself.
Is FBI going to ask a backdoor in every safe and door, because inside it or behind it there could be an evidence, or a crime is being committed?
Sure, just like technology can help investigations - think DNA - it could also make them more difficult, especially if law enforcement agencies chase the 'easy way' and don't get prepared for the difficult one.
Or they believe they could also enforce US backdoors in foreign devices? Or once the backdoor exists, refuse to give the key to some countries were it takes very little to be declared an enemy of the state and searched? What if some mobe, even of foreign citizens, is inspected in countries where, for example, homosexuality, or even carrying some books is a crime?
I may understand FBI fears of being unable to gather evidence. But tha is a risk that always existed in a democracy. Better they stop asking for a dangerous, unlawful easy way, and invest in training to better investigation techniques.