Many smaller public groups have a large number of "lurkers" whoI prefer the idea of voluntary donations, but if the group owner wanted to make donation mandatory then I'd say "absolutely".
In fact, were I an owner of such a group I'd be more inclined to give a "sweat equity" discount to the members that *do* participate. They are the ones adding value to the group, the lurkers are not.
Of course, the above depends entirely on the culture and purpose of the group. I don't mean to apply a one-size-fits-all solution across all the different styles of groups that exist.
Others are not financially able to do much more than exist and use theWhich is why I prefer a voluntary donation policy.