You can start here: https://en.wikipedia.org/wiki/Nuremberg_Code#The_ten_points_...
Specially point number 1. Also read on the history of Nuremberg Code and why it was triggered after WW2.
Also you could read this explanation by a professor of law at U of Maryland http://laboratorium.net/archive/2014/06/28/as_flies_to_wanto... which talks about Facebook research which is similar to this one.
In general: you are tricking the end user, this is not a simple A/B test this is more of here is a company that does not exist providing nothing but let's see how you react to it. Today is fake pizza, tomorrow is a fake HIV med that cures it in one day (you click on it, there is a strong inference that you have it), etc the possibility is endless. Who is deciding this? That's why I mention ethic panels or regulation or whatever way of putting limits on it.
The only good thing here is now we know that we are test subjects when using Youtube/Google.