I'm not making a stand on the reward vs punishment debate. I'm generalizing from my personal experience - that is, if I couldn't lurk or make posts on lesswrong, I wouldn't be interested in FAI at all. If it were the case that the minimum amount needed to participate in rationality topics that LW discusses was "read and write academic papers or participate as a volunteer or worker in MIRI", I wouldn't be making any sort of effort along this axis whatsoever.

Plus there's the whole cult-aversion thing - punishing those who buy in to EA but do not make as much effort as you want them to carries a whole host of bad connotations.