Some very authoritarian arguments and assumptions in play here.
The author states: "Taking a step back, it's fair to say that the majority of law-abiding citizens would want prosecutors to be able to access evidence that could help convict someone of a serious crime, regardless of how strongly they feel about their own personal privacy."
I disagree. I don't think the majority of citizens - "law abiding" or not - want the police to have any more power than they already do. A vocal minority of people trust the police. Most don't. And the police, spooks, governments and so forth haven't been doing anything to regain the trust they have lost. They can't be trusted with the power they already have. There is no reason whatsoever they should be allowed access to the treasure trove of information on our phones.
Why, you might ask? Because of the silliness of the concept of "law abiding" (shall we play No True Scotsman?). Nobody is law abiding. NOBODY. Every single one of us commits multiple infractions of the law every day. The laws are designed like this. Not only can no one person know all the laws to which they are supposed to be beholden, but many of those laws are contradictory or criminalize ordinary everyday activities.
Phones and computers contain us. Our lives in all aspects. If there were some means by which it could be assured that law enforcement agencies - from the NSA down to the local bylaw cops - were only allowed to search phones when they had a damned good reason to believe that level of privacy invasion was warranted, they had a judge signing off on it and there was layer upon layer of oversight...maybe - just maybe - we could all meet in the middle and talk about this like adults.
Unfortunately, no such means of restraining the police exists. They are too powerful, politically, for anyone to rein them in. We've see that over and over and over again, in all western nations. Cope in the US roll on out of a cruiser in response to a call and in one fluid motion murder a 12 year old boy in cold blood. No calls for him to surrender. Nothing. Why? He was playing with a toy gun in a park. They get away with it. And then the city sends the family of the murdered child a bill for $500 for the ambulance.
If police have the capability to pwn a phone they will use it to go fishing. They will use it without oversight. They will use it without warrants. They will use it to investigate every tiny crime and misdemeanor in an attempt to fine evidence - any evidence - of further things they can nail someone with.
And they will! Every single one of us, as stated above, is guilty of something. And our phones probably know what. How can we, as a society, justify handing over that level of power to an unaccountable, unrestrained and massively corrupt group of law enforcement agencies who have every interest in ruling their communities and absolutely zero interest in serving their communities?
In addition to the above, there is a quote from Generic Corrupt Cop #42: "If Apple can refuse lawful court orders to reasonably assist law enforcement, public safety will suffer. Crimes will go unsolved and criminals will go free"
So his argument - and that of authoritarians everywhere - is that it is perfectly fine to remove the presumption of innocence in order to catch the guilty. This is wrong.
It is, in fact, better that a thousand guilty men go free than one innocent man be punished for a crime he did not commit.
Giving the cops unrestrained access to our personal lives gives them the power to go fishing to invent things to crucify us with. They can - and they will - use that power injudiciously, to further prejudice and as a means of punishment against dissidents and dissenters.
Unless and until we can solve the problems inherent in the schism between the people and those who are supposed to serve them we should absolutely and emphatically not be granting our self-styled masters yet more power over us.
Fix the system first. Then we can talk about letting that system see everything we've ever done, or ever will do.