https://upload.wikimedia.org/wikipedia/commons/c/c7/Prism_sl...
Also, I don't think any number of people believing to any extent that a corporation may have been compromised removes an important incentive for that corporation to maintain its integrity. For a security-conscious company, reputation and trust don't go that far so it would be safer to assume that Apple can be or has been compromised maybe even without their knowledge. That company would have to look after its own security and use custom protocols / devices. If it was forced to trust Apple, it would have to find an ingenious way to ensure that was not at all in the interest of Apple to betray them.
The FBI is not the NSA.
The fights that we know about can be nothing more than a marketing stunt. They were what Apple wanted public to know; when leaks happen that Apple doesn't want public to know, Apple's "commitment to privacy" rather pales. Apple was listed as a PRISM data provider, they were accused in using their employee's message data against them. Now they also admit to looking into iCloud photos.
FWIW, I am rather skeptic. And I even have reasons: if the NSA has the power to coerce, Apple wouldn’t repeatedly gotten into fights with the US government to unlock iPhones.
Cooperating with the NSA is also clearly not in the companies’ interests. If (when) it comes out, they’d be at risk to lose a lot of business in other countries.
In any case, my usual argument about cynicism applies: spreading such theories becomes self-fulfilling, because why should MS work for the NSA/every politician take bribes/every cook spit in your food, if that’s what the people believe anyway, no matter what you actually do?