posting is also important because SOMEONE has to generate the content for others to read.
That is precisely the wrong reason to post something. We are not starved for content. What we do lack is a high signal-to-noise ratio, and the original point was “how do we increase the signal?” The assertion then is that lurkers only post when they find something genuinely interesting and high value to say. (Whether and how this point could be disproven is left as an exercise to the reader.)