Crowdsourcing/Community design/A shared goal

Wikipedia’s core principles are summed up in "five pillars" which all new users are encouraged to learn. A quick summary is:

Wikipedia is an encyclopedia
Wikipedia is neutral
Wikipedia is free
Users interact in a civil and respectful manner
Wikipedia does not work on fixed rules

Which of the pillars is the crucial one for getting people to work together productively, and to discuss each other’s work constructively? The fourth pillar may stand out as the obvious answer because it directly tells users to be civil. However, such rules do not guarantee civil behaviour, or the problems with trolling and abuse in online communities could be solved instantly.

More important is the first pillar, “Wikipedia is an encyclopedia”. This specifies a very constrained kind of literature; an encyclopedia is a summary of already-published knowledge. New users who add personal opinions, personal experience or speculation are told that this is inadmissible irrespective of whether they are right or wrong, because those things are not in scope of an encyclopedia.

If the goal of an article about abortion were to decide “the truth” about abortion, the debate would be unproductive and interminable. In practice, this would not be a shared goal because people would work against each other. Deciding what reputable sources say about abortion, and what opinions are held about abortion by different cultures and groups, is more achievable. There is scope for disagreement, but it is a goal that people with widely different opinions can share.

The drive for quality requires that articles are written in a balanced way, and writing a balanced article usually requires multiple sources and points of view to be represented. This incentivises contributors to write about perspectives that they don’t personally agree with. Paradoxically, the focus on verifiable sources can give the impression that Wikipedia is not interested in or directed towards truth, but this focus actually promotes reliability by directing contributors to reliable sources rather than their subjective responses to the topic.