I'm not necessarily of this opinion, but his view is that knowing what you had for breakfast and your address is the same as your bank account # or house keys; it's just that people haven't realized this yet.
Their argument is that the reason why people say house keys, or bank act # is different is because they are protecting something of value. His argument is what you do on a daily basis is just as valuable you just don't know it yet.
The other argument against is "yes my privacy/ daily activity may have 'value', but unlike my bank account or house keys people can't take something from me from knowing it. "
That's more up to opinion, but the argument is knowing you so well, someone can take your independence. A bit dystopian, but imagine n years from now, ML is good enough to predict your responses and behaviors to 80+% of things. Companies now use it to effectively get you to make decisions they want. Combinations of timing, placement, location, repetition, persuasion, counter-argument all to produce a desired result, but unlike present day extremely effective and possibly without your awareness. If there is a way to get our wet ware to do it, ML will figure it out.
Advertising/Marketing/Sales become a game of Go, where you're the Go board. Best ML wins.
We like to think we're fully in control of our decision making facilities, but study after study shows that's mostly an illusion. Our sub-conscience mostly decides for us, and then our brains rationalize this away after the fact.
The fear is that by giving away your emotions, your responses, your ocean 5 factor model, your preferences, your habits, and a playground to test all of this in you are potentially giving up your independence at a future time.
It's all dystopian, it's not guaranteed, but it pans out as all likely directions and very probable tech.