I suppose the easiest means of discrimination is imagery. Having said that, everything is on a continuum, right? An erotic passage needs reading to determine it's lasciviousness, whereas a pasted image will instantly be presented to the viewer. But, again, I may have a 'line' drawn much closer to beginning of the continuum than the next. Context is important, too, eh. It may seem a pointless differentiation, but at least with smut that adheres to a particular communities 'rules', i.e. cosplay or whatever else exists close to that milieu, may have at least a semblance of what acceptable or not. Smut for smuts sake is porn in my view and as people have stated, there's enough of that on the internet.

I guess in short, people can police themselves, I suppose.