To do any scientific research on any subject - any random subject whatsoever - you first need to define the subject.

So that is the first obstacle - porn is hard to define.

Pomegranates and fish oil, by contrast, are easy to define, and we all agree on what they are. Still, even fish oil can be in capsules or in liquid form and pomegranates can be fresh or juiced or packaged in capsules, and those differences present difficulties.

Porn is much harder to define than fish oil and pomegranates.

So if you want to find scientific research, the first step is to see if scientists have been able to agree on the scope of the research.

You cannot do any research without first agreeing on the scope of it.

In general, you cannot do any project without first defining the scope.