When I see the word "volunteer" in a response to a sensible critique of FLOSS software, I rankly speculate that a deep design flaw has manifested itself as a social problem.
It appears I am right in this case.
Are there known cases where I would be wrong?
I agree with you in general though. I think Wikipedia would be the exception.
This is a great system for an encyclopedia that must find the best approximation of the truth, but I wouldn't call it "incentive free". Similar incentives in the social world (pushing out people that don't conform to the moderator's world view) could be disastrous.
For example, I don't think they used the term "volunteer" in their funding drives. Maybe that's for obvious reasons, but I also don't remember seeing "volunteer" when reading about their approaches to page vandalism, editors abusing power, etc.