Should participation be voluntary or compulsory?

In general, it is much better to let participation be voluntary. This way, communities of practice live on because they create value for members, not because of an edict or a box to check. It does not mean that one cannot strongly encourage participation or even request that someone run an idea by the relevant community. But making participation compulsory more generally runs the risk that communities become just another meeting to go to and survive. This is likely to deflate the very social energy that makes healthy communities of practice places of meaningful learning.