I have problem pointing out precisely what exactly that aspect would be.

You can continuously watch porn in the same way that you can continuously play World of Warcraft. You can't continuously masturbate in the same way that you can't continuously eat pizza.

"Porn" is too vague. Are you talking about a quick 5-minute session or a marathon lasting several hours? If you've never done the latter, consider that some people might. The effects of the two are likely to be quite different, especially if the latter is a frequent occurrence.

Also, it's not at all popular among my friend groups to slander porn. That's seen as sex-negative, which is one reason I never got around to thinking about porn as potentially harmful until quite recently.