The point you are missing is that there was no cambridge analytica app and nobody opted into it an app that doesn't and didn't exist. They opted into a completely different app that datamined it for completely unrelated purposes and then, much later, sold off to CA which used it to target people. one was on the up and up and one was CA. Again, if trump did what obama did on the level it would have been fair game. they were shady and used shady tactics and shadily acquired data. Not a single person that opted into the koger app thinking it was a political app but people that used the obama app knew what they were getting into.