I do not know where to begin to answer this. How about a simple truth that Apple is not "forced" to do business in the United States, for starters?
Just because an entity does business in the United States does not mean you can force them to create a product that doesn't exist. I have managed many construction projects for the government but I am under no contractual obligation to do any work for them currently, should they be able to force me to work on a current project since I've done similar work for them before? Of course not, I can (and should) be able to tell them to pound sand if I so desire.
I do not trust the government. I argued in the past that we were giving up to much liberty interests to terrorism. There were lively discussions here and elsewhere, but the bottom line is that American people chose to live with the surveillance at the cost of their liberty. If Americans thought otherwise, Patriot Act would have been repealed; NSA would have been defunded; Edward Snowden would not have had to flee; FISA court would have been shut down and the judges who wrote secrete opinions would have been impeached; Guantanamo Bay would have been a history. The list goes on.
When it comes to security and privacy, the question comes down to where we draw the line. It is a compromise, and we redraw the line as needed. There will never be an absolute line. (the 4th Amendment speaks of reasonableness) The hypo you imagine is, in some circumstances, already a reality; All cars sold in the U.S. must be equipped with GPS, and the government can monitor the GPS with court-issued warrants, thus tracking the movement of the drivers. But I highly doubt we will have to wear cameras in our homes anytime soon, if ever. Why? Because I am confident Americans will not tolerate such a law and its enforcement.
And to date there is no law that requires software makers to include or provide backdoors to their encryption. Until such a law is passed by Congress I don't see how this is remotely legal and I'd still question the constitutionality of such a law. Since no such law exists that is a debate for another time.
So the situation in which I find myself is not something I hoped, but it nevertheless is what my fellow citizens decided in an ongoing debate in which I participate. I continue to advocate for greater privacy against government's watchful eyes, like you do.
None of this gives Apple a privilege to be exempt from the laws that you and I are subject to. And I trust Apple even less than the government. Case laws dictate that those who facilitate crimes, even if they are not guilty themselves, are are required to produce evidences as necessary. This is why there is no "Swiss bank" in the United States.
P.S. Again, I really am not sure if you are serious about your slavery argument.
Let's try a hypothetical, let's assume that there are two people that wrote the encryption code for IOS that the FBI wants to circumvent. These are the only two people in Apple's employ that can write the code that currently doesn't exist to comply with the FBI's request. Now let's assume that they quit Apple in protest and refuse to provide labor to circumvent the code. Does the government, in your opinion, have the power to throw those two people in jail until they agree to provide their labor to the government even though they are under no contractual obligation, have committed no crime nor has Congress, to date, passed a law that requires them to do so? If so, how is that not involuntary servitude which is expressly prohibited by the 13th amendment? If it's not involuntary servitude what exactly would you call the forcing of a person to provide their labor to the government against their will?
This would be a different story if the government could prove that Apple already developed the software and had it in their possession. I would argue that the case that you cited might work if the FBI writes the software themselves and then requires Apple's assistance to install it. In the case you cited the Feds wanted to install their own device onto existing infrastructure, everything that was "new", in this case a pen register, was provided by the Feds. Like my own personal example above, if they can force Apple to create something that doesn't exist why can't they force me to work on a future construction project? Also, does that "force" extend to the men on my crews that worked on previous .gov projects regardless if they are still my employees or not?
Another question, do you think that the Federal Government has the lawful ability to force Phil Zimmerman, the original author/developer of PGP, who no longer works on the PGP project to write and release an update that gives the FBI a backdoor to PGP? If so, what penalties do you think the government can impose if he doesn't comply? How many hours a day do you think they can, or should be able to, force him to work?