Is it because the labour is unpaid, people think their contributions are equally as valid, or even proportional to the effort they put in? Like when someone volunteers for a charity/nonprofit but does a shit job and you have to ask them politely to stop.
I don't think that's really a huge factor, based on my many years doing all sorts of volunteer work. These kind of small conflicts happen all the time in all sorts of contexts. The thing that makes Wikipedia so difficult is there is no one with any authority to tell people to knock it off (or rather, things need to escalate quite badly before someone comes in and does so). At your job there's our boss or whomever, and even at many volunteer jobs there's often someone who intervenes at an early enough stage. This is also why small conflicts between neighbours can escalate so bewilderingly spectacularly in ways that can be hard to understand for onlookers.
