Well, part of the concern is that there was access provided without clear oversight on how they were going to use that data. This is one of the things that's creating a challenge for academic research too. Facebook and many other social media platforms have tightened up their APIs and their data access. That was often done without much transparency—and that's what Facebook has admitted—about how that data was going to be used, so I think it's twofold: it's basically knowing who has access to it and also making sure they're subject to accountability about what they're doing with the data.
On September 25th, 2018. See this statement in context.