Preamble to the U.S. Constituion on iPhone 6
App: Constitution for iPhone and iPod Touch
If you love the constitution, the right to privacy, and America, you should support Apple against the government's push to destroy your civil liberties. Although there are many technical nuances that can mire down the discussion around this issue, 3 tried and true constitutional arguments against eroding our civil liberties apply to this case just as they have to many other civil liberty struggles of the past.
Argument 1: The same one pro-gun folks use to support the 2nd amendment.
You remember this old pro-gun chestnut, right? If you make guns illegal, only the bad guys will have them. Well that applies 100 fold more to encryption.
If you allow the government to force Apple to put in backdoors or make tools to crack the iPhone, you simply take the right to privacy away from law abiding citizens. Terrorists will just use one of thousands of other encryption apps out there. If you search the free open source software repository GitHub, you'll see the dizzying array of choices readily available.
Free source code and apps for all manner of encryption services are already out there, and nothing the government can do will stop terrorists or anyone else from using them. The genie is out of the bottle, Pandora's box has long been opened, and the horses long ago left the barn with regard to encryption.
Some people just don't get this, but the terrorists do. If the government wins against Apple, law-abiding citizens will have lost their right to privacy, while the bad guys will be free to communicate with impunity. It's just that simple.
Argument 2: What's good for the goose...
If you unlock this iPhone, you will have unlocked all iPhones for everyone forever. The government has done a really bad job of lying, saying this is just about one iPhone, yet it has already lodged requests to unlock 12 more. So this is clearly not about just one phone, it's about all iPhones, and the government's blatant lying makes that abundantly clear.
Further, considering how the government has botched its chance to get at the terrorists iCloud backup of the iPhone, and a former director of the NSA and CIA is saying the government is wrong on this, it's pretty good bet that Apple knows better how such a backdoor crack would apply to and compromise all other iPhones.
As such, once the iPhone is cracked, yes, today's White House may use the crack to gain access to this terrorists' iPhone today, but every other administration in the future—someone more like, oh, say, Joe McCarthy, J. Edgar Hoover, your spouse's divorce attorney, or worse—will have the ability to abuse that power tomorrow.
Argument 3: The right to privacy is like the freedom of speech...
The ACLU and even citizens that were targets have defended the free speech of hate groups in our country. The ACLU and our country has defended free speech for the KKK and even Nazi groups in the past, not because they were sympathetic to that speech, but because once that right is eroded for anyone, it can and will be destroyed for all.
As the ACLU said, "If we don't protect the free speech rights of all, we risk having the government arbitrarily decide what is, or is not, acceptable speech."
As over the top hyperbolic as this seems, the country was built on the principles that life and, obviously safety, are secondary to our civil liberties.
"I disapprove of what you say, but I will defend to the death your right to say it." --Evelyn Beatrice Hall
In following those principles, one mother of a San Bernardino victim supports Apple in maintaining our right to privacy, saying:
This is what separates us from communism, isn't it? The fact we have the right to privacy. This is what makes America great to begin with, that we abide by a constitution that gives us the right of privacy, the right to bear arms, and the right to vote.
In other words, just because idiots want to speak, doesn't mean we should destroy our own freedom of speech. That's a bit cutting off your nose to spite your face. Similarly, just because a few horrible idiots use iPhones, does not mean we should destroy our civil liberties.