Yeah, the unequal bargaining power between the company and the candidate is a real problem. Even if the company makes providing the access information optional, there's still a kind of invasive coercion happening.
That said, companies have been requiring that applicants submit credit reports for a long time, so the idea that there's a bright line between what's "private" and what's "public" when it comes to employment isn't quite right.
I once worked for a company that did a lot of military contracts. They would ask some of us to get security clearance to be able to work certain projects (and enter the 'secret room'). It was still optional and I never felt it pushed on me even though it would have had career benefits. I opted out because the requirements and paperwork were nuts and part of the deal was that the government would potentially track whenever you left/entered the country and a whole bunch of other things.
I thought this was a really nice way of letting your employees have a choice even though in this particular case they probably could have forced everybody to do it. Now you have companies which do not really need to have this personal information asking employees for it. Here's the thing though. If my employees had lots of nasty things to say about my company then my reaction wouldn't be to stop them by monitoring everything they do. Wouldn't you want to try and fix the problem?
That said, companies have been requiring that applicants submit credit reports for a long time, so the idea that there's a bright line between what's "private" and what's "public" when it comes to employment isn't quite right.