No - it's binary
There are no shades of grey here. Either you have secure data or you don't. Once you create a backdoor into a system, unlock just *one* phone, make just *one* exception for law enforcement or whoever, THAT IS IT. There will be no going back:
a) once the vulnerability is made, do you really think it will stay in the hands of "the good guys", even if they were the ones (whomsoever they may be) for whom it was specifically created?
b) once the precedent is set so that "the good guys" (whomsoever they may be) can get the information that they want, do you think that others will not seek to use whatever means necessary to avail themselves of this, whether by rule of law or commercial pressure or some other means?
It's binary, people - being referred to as "West Coast law" in some articles I've been reading.