This part is pretty new. I wonder if my former colleagues have done any FOIA work looking into how travelers' disclosed social media accounts have been reviewed or analyzed!
It's reasonable for a country to want to know if you're likely to abuse your visa.
Eg your socials might show you are a professional paid speaker at conferences. If you applied for a tourist visa that would be reasonable to flag you and ask you if you have paid gigs on the wrong visa.
Europe will also ask the same questions for foreigners. If you're a young woman travelling on your own you can expect questions to challenge if you might be earning money as a nanny on a visitor visa. Checking their phone messages to see if they've been making arrangements to this effect is a very straightforward way to determine intent.
The problem is that giving the capability, initially for "reasonable uses", also makes it available for unreasonable uses. That's the banality of evil - dystopias are built one "reasonable" step at a time.
For the conference case much more reasonable would be to make the organizer and anyone profiting from the even liable for having speakers without a proper work permit.
You can solve these things sufficiently without reaching for the panopticon. As more of our lives are moved to the digital world its very important that we don't give up rights that we previously had in interactions that weren't assisted by technology.
There's no chances I can remember them all, especially as I've been contracting and get a new email every 3-4 months or so.