Discussion question

This study has been HUGELY controversial and criticized, primarily over questions of consent.  The debate has centered around whether it is okay for Facebook to conduct such research on its users, without giving them the choice to opt out… Critics of the study argue this is an ethical violation, Facebook argues that users agree to their policy acknowledging data can be used for research. 
What are your thoughts on the ethics of this study? 

https://www.theatlantic.com/technology/archive/2014/06/everything-we-know-about-facebooks-secret-mood-manipulation-experiment/373648/