In December 2009, Facebook changed its website so certain information that users may have designated as private – such as their Friends List – was made public.
They didn't warn users that this change was coming, or get their approval in advance.
Facebook represented that third-party apps that users' installed would have access only to user information that they needed to operate. In fact, the apps could access nearly all of users' personal data – data the apps didn't need.
Facebook told users they could restrict sharing of data to limited audiences – for example with "Friends Only." In fact, selecting "Friends Only" did not prevent their information from being shared with third-party applications their friends used.
Facebook had a "Verified Apps" program & claimed it certified the security of participating apps. It didn't.
Facebook promised users that it would not share their personal information with advertisers. It did.
Facebook claimed that when users deactivated or deleted their accounts, their photos and videos would be inaccessible. But Facebook allowed access to the content, even after users had deactivated or deleted their accounts.
Facebook claimed that it complied with the U.S.- EU Safe Harbor Framework that governs data transfer between the U.S. and the European Union. It didn't.
While you can abstain, it creates all kinds of awkwardness that I'm not willing to deal with currently.
However, what Facebook did is far worse than violating that agreement. Facebook gained accessed to user data on third party systems, to which they should never have had access. They gained this (unauthorized) access (at best without clear consent) on a false pretense (disguising as security related requirement). Then they imported user data, with no relationship to their stated goal/requirement, into their platform.
Associative contact information is a highly valuable commodity to any company involved in marketing and social media. I've seen a lot of people argue how this could have been the result of a laps of oversight, but that sounds like arguing how a gem stone trader might have "accidentally" stolen a large quantity of rough gem stones, while claiming to not have known their value. Even if theoretically possible, it's extremely unlikely that nobody within Facebook knew/realized the value of this data.
Either way, Facebook gained access to highly valuable assets. Even in the unlikely event of sincere lack of oversight, it would demonstrate a level of incompetence that warrants them to still be held criminally liable.
Moreover, Facebook might actually have outright violated the Computer Fraud and Abuse Act (CFAA), in particular the "access in excess of authorization" part, but I'm not sure.