The terms restrict scraping without permission. I'm pretty sure that the FBI would be able to find a way to get Fb's permission. And for good reason. Again, it's public information. No harm done.
It is fine as long as other companies/startups are granted such access. The problem here is if FBI can wield a bigger power in getting this access, we have a problem. Not so much with the data itself, but the spirit of how someone with power can get their way.
Isn't that sort of the definition of power? The ability to influence more than others? Reputation and relative influence are zero-sum games.