Based on this answer, and the fact that the discussion was said to get off topic and I wanted to know more, I thought about asking this question to find an answer.
It seems to me that both campaigns used data that was obtained without the consent of the vast majority of people:
From Politifact
The Obama campaign and Cambridge Analytica both gained access to huge amounts of information about Facebook users and their friends, and in neither case did the friends of app users consent.
And then later:
Whereas the data gathering and the uses were very different, the data each campaign gained access to was similar.
So my question is: did both sides basically do the same thing (using data without the users' consent), but Facebook only got "called out" when the Cambridge Analytica founder blew the whistle?
I would like to make one thing clear as far as I understand it. Both camps started by getting user data from users who willingly used their app. Then both campaigns used the data from those users to get the data from all the users in their contact/friend list as well (without consent from those friends), bloating the original amount of data x100.
Some information from this article:
the Obama camp used a common Facebook developer API–the same one used to access the data for Cambridge Analytica–to create a Facebook app that could capture the personal data not only of the app user, but also of all that person’s friends.
and this
The Obama campaign’s director of integration and media analytics Carol Davidsen said on Twitter that Facebook was surprised to learn how much user data could be pulled out through its graph API. “We were actually able to download the entire social network of the U.S.
It feels to me that the Obama campaign did not do anything wrong as such - Facebook is to blame for not protecting the data. But (like my question), if both sides did the same thing, then one could also not say that CA did much wrong.