Lurking is among the deadliest toxins of community formation and collaboration. By their silence lurkers leave other collaborators fully in the dark. Is someone inactive, or actively listening?
There's an easy antidote: Being social.
Giving a simple token is often already enough. It takes 2 seconds to indicate "not interested" or "no time".
This is not impolite, more like the opposite: A courteous gesture to let someone know to not waste time on you on a particular matter.