I'm not sure it would matter. The general population that compose Facebooks revenue stream don't seem to care. We keep hinting at these ethical conundrums that invisibly regulate massive businesses when they simply don't. It's not just tech, it's big businesses in general. The ethics only matter if a large enough population of the consumer and product base both care and act. Only demand matters and if demand doesn't care or you can manipulate the demand not to care, you can get away with about anything that isn't explicitly illegal.
I suspected Facebook does the work you referenced but I had no idea they actually did and had any flack about it. I'd like to think I'm a fairly tech savvy and an informed consumer (especially around issues like this), maybe I'm not, but if I am, what hope do you have of the general population caring when they aren't even aware as a first hurdle before the other massive hurdles of getting them to care enough to act.
The fact is that this type of work isn't regulated. Funding agencies regulate human subject work for your typical public funded research work and require a lot of informed consent. The leverage they use is that should you violate these terms, you may have current and future funding pulled, may be black listed across multiple agencies, and may find it difficult to pursue any career in research in the future involving human subjects. There are lots of disincentives not do this on the premise of manipulating your resources.
Meanwhile, entities like Facebook have piles of such resources and have a vested interest in all sorts of this questionable work. Pretty much nothing prevents them from doing it since they're self funding. Unless you can remove their self fundability, it will continue. This goes back to problem of needing consumers to vote with their wallet in an effective manner.
The other option is to create the explicit policy protections in law to regulate these activities but as a society, capital has convinced everyone that all regulation is evil and will only hinder consumer/citizen progress. You need not only policy but real enforcement teeth as well that create disincentives that are catastrophic enough not to tempt risk for the potential gains.