First, if the conclusions are counterintuitive or unexpected, then when you look closer, you will find that the methodology is garbage and that it does not support the conclusions given.
Second, if the conclusions reflect things that you believe are true, when you look closer, you will find that the methodology is garbage and that it does not support the conclusions given.
If you have specific criticism regarding the methodology of this study - which doesn't, prima facie, appear unsound - please let the rest of us participate.
"The have used a correlational model, not a causal model. There are several confounding variables the paper doesn't consider, hence it is not proven from the evidence that Facebook has a negative impact "
The article discusses how the study looked at different universities during the same time period, some of which had access to facebook and some of which didn't, and discovered that in the first case there was an increase in mental health issues over that period. There could still be confounders, sure, (or the sample size could be too small etc.), but at a first glance, that's not an unreasonable approach, as it tries to isolate the variable "facebook yes/no".
That said, if you haven't read the article, I'm not sure why you even felt the need to comment? This is exactly the same kind of shallow dismissal I was calling out.
I agree it's not unreasonable, but you have to account for the fact that back then, most of the colleges that had it were top tier/high stress/highly selective colleges. Facebook started at Harvard, then went to Yale and Princeton, and then on to basically most of the US News top 50.