When I ran a forum I got so sick of people who offered nil input and only read the posts without leaving any comments whatsoever.
What we did was to warn those members that if they didn't start posting they would be deleted.
It was surprising as most started to get involved and started to at least comment on posts.
Those who seldom logged in and or failed to post were eventually deleted after a number of warnings.
Not that it really matters to anyone, however, unless things improve and I am not having to keep replying to my own posts, I will be gone.