You make the mistake of assuming the watchmen have and will always have noble intentions. Rather, you should assume that at some point, someone in power will have the most ignoble intentions.
What do you think the negative consequences are for a government to have a permanent record of every private conversation made over the Internet? Bear in mind that the fraction of all private conversations which occur over the Internet is only increasing.
You must assume that "exceptional access" really means "routine access". While the government claims it only wants access to some encrypted content, decryption leaves no trace. The NSA's collection posture is: "Sniff it All, Know it All, Collect it All, Process it All, Exploit it All, Partner it All." Does it sound to you like the NSA will sit on their hands while some other USG functionary has the Golden Key?
> Nobody really cares about your personal Facebook messages to your friends and family. You're not that important. But still considering what is being offered in payment for this privacy, it's still worth it to you?
Perhaps you're correct now. But imagine that a decade from now, you (or a friend or family member) become an activist or a political candidate. Now your incumbent political opponents have a wealth of sensitive private data to mine to find anything to imprison or discredit you. The argument extends further than your own direct interests: What happens to our political system when policymakers are completely transparent to the NSA and their political co-conspirators?
Considering the very real risks of a totalitarian government ruling with an iron machine learning model, or a silent coup by military intelligence, is it still worth it to you?