If you pull in ethics (rather than law), let me tell you straight off that I have little expectations for that mechanism to suffice in the marketing space (there is a constant race-to-the-bottom amongst marketing companies, making it hard for those with a higher ethical stance to survive at the moment). Nevertheless, it is worth remembering that ethical action in a position of power always requires considering the weaker point of view first.

There are, as I have hinted before, several levels at which I think things are wrong:

• information imbalance (squared): the car salesman who hires a PI ahead of time and knows your weaknesses does not just have more information than you have about them. He has more information collected in ways you would have never imagined, at a level of intrusion you would have never imagined.
• in politics, it hurts the debate: Brittany Kaiser (Director of Program Development, Cambridge Analytica & SCL Group) is on record saying: You’re really catering to the fears they already had… It’s not really making them more scared or insecure than they already were. How can this be defended? If you use those techniques in politics, and make divisive appeals to emotions around deliberately false facts, it is very damaging to the public debate. It turns into something like distributed gas-lighting.
• Facebook: individuals have delegated some of their filtering intelligence to Facebook over time. Facebook does the curation for them, and injects into this feed some advertising. Facebook has obligations of transparency (we allow targeting based on these criteria). Of course, Facebook is already far from doing a stellar job there, but assuming everyone understands this, there is another leap here in targeting based on gullibility, and possibly introducing deliberately misleading content.