The issue was never that CA did this with "false pretences" (they didn't sign up users directly, that was done by an academic who then sold the data) or that by signing users up on your own website, you were doing some above board. The issue was that Facebook allowed access to not only your account but your friend network. That was what Obama used, that is what CA used, that is why both tried to get the Facebook login, and, btw, the end goal was exactly the same: microtargeting of ads.

Btw, there are probably hundreds of other companies who are doing the same thing. A lot of the "data science" startups are using this data in their products, there was an Israeli startup (mentioned here recently) that somehow had click data from Google, individual search data from Google...this isn't just politics, this personalised, identifying data that is somehow everywhere.