I’m not sure how you’re using the term here, since I know two definitions for it:

A) streetcorner loiterer

2] slang for testicles

Eiither are you talking about lurkers, or trolls, or shitposters, or what?

Lurkers may or may not be necessary. I’m not one, I couldn’t say.

Trolls are not necessary, and in fact harmful to discourse.

Shitposters are very necessary, they are the leaven to discussion that makes it fluffy and digestible.