It's not, of course, literally in the Constitution that you cannot encrypt things and then refuse to decrypt them for law enforcement. Nor is it in the Constitution that people selling encryption devices must include backdoors.
What words in the Constitution do you see as pertaining here?
Of course you can encrypt things yourself, and I would imagine you could probably refuse to hand over the password under your 5th Amendment rights. Nothing's changed there.
I think the issue here is that someone else (Apple) has gone and set up an encrypted environment for you in such a way that actively prevents law enforcement from carrying out legal investigations with a warrant on an incredibly popular series of devices that they were capable of searching before. Let's face it - the number of people who are buying iPhones because they are now encrypted is miniscule. If you really wanted to encrypt all of your data, optional full disk encryption already existed on other phones. The problem the police have with it is that it's now set up by default, they can no longer access it when they do have a valid warrant and this extends to everyone instead of just the handful of criminals that would take extra steps to encrypt their data. John Q. Criminal didn't choose to encrypt his phone, Apple made that decision for him.
Not at all true. The fifth amendment doesn't mean the court can't serve you with a subpoena for your device's unencrypted contents and imprison you until you provide it, for life if necessary.
[1] http://cyb3rcrim3.blogspot.com/2010/04/passwords-and-5th-ame...
[2] http://cyb3rcrim3.blogspot.com/2009/03/5th-amendment-bummer....
Why give law enforcement the ability to arbitrarily circumvent these protections? If the court says, "No, the defendant doesn't have to give it up." Why would you want to have a mechanism in place for the prosecutor to say, "Eff the court, we're taking that information anyway."
I'm no lawyer, but I suspect any evidence gathered that way would be thrown out anyway.
Likewise, you've always been able to encrypt your phone/computer/etc., and for the most part the police aren't able to decrypt it so long as you encrypt it properly. Nothing's changed in that respect. It's not a common enough phenomenon that an inability to decrypt some laptops will affect most cases.
The iPhone issue is different, though - it's not the user choosing to encrypt the device; it's Apple choosing to encrypt the device on the user's behalf. This won't affect the search of just a few suspects' property. Due to the popularity of the iPhone, it will likely affect conducting searches for a significant percentage of cases that wouldn't have been a problem before the last update to iOS. The police already needed a warrant to gather any evidence off of your cell phone, anyway; now Apple has gone and effectively stated that the warrant doesn't matter, the police don't have the right to search it to begin with.