Vandalism on Wikipedia is a deliberate attempt to compromise the integrity of the encyclopaedia, often through the insertion of obscenities, insults, nonsense or crude humour, or by page blanking.

In the early days of Wikipedia, vandalism was a very serious problem, requiring time-consuming effort by volunteers; this led to restrictions on editing which prevented certain forms of vandalism from occurring, but which also involved negative side-effects. In recent times, the ingenuity of our coders and diligence of our vandal fighters have led to new, faster and more effective means of combating vandalism, without some of the negative side-effects of restrictive measures.

As the problem of vandalism becomes decreasingly significant relative to other concerns, we should give it a decreasing level of consideration relative to other concerns when deliberating on the value of proposed counter-vandalism measures.

Thanks to the development of increasingly efficient tools for identifying and countering vandalism, and to the eternal vigilance of Wikipedia's dedicated corps of vandal-fighters, blatant vandalism is much less of a threat to the integrity of the encyclopaedia than before.^[1] The paradox of counter-vandalism efforts is that the more successful they are, the less priority marginal improvements to them should receive, relative to competing priorities.

Highly active Wikipedia editors and administrators frequently encounter vandalism through monitoring recent changes, new pages, reporting pages or administrators noticeboard. This monitoring means that such editors, who also form a large constituency of those active in determining policy, are exposed to vandalism to a far greater degree than exopedian editors or the encyclopaedia's readers are.

The natural consequence of influential editors being routinely disproportionately exposed to vandalism is that there may develop a systemic bias over-estimating the importance of combating vandalism relative to other aims of the project; a siege mentality, in other words. Although Wikipedia is putatively an encyclopaedia that anyone can edit, vandalism concerns have been used as a rationale for restricting the editing privileges of anonymous users (e.g. through semi-protection and autoconfirmation requirements) and increasing the difficulty of using free content. While these specific instances may be appropriate measures, it is important to weigh the benefits of anti-vandalism measures against the negative consequences of making certain means of contributing positively more difficult.

The positive outcomes of more restrictive counter-vandalism measures are clear – decreasing vandalism; the negative consequences can include a more hostile reception for new users who are experimenting or unfamiliar with the way Wikipedia works, discouragement to editors who find that their good-faith attempt at improving a protected page is unwelcome, and compromising the founding principle of a free, open, ahierarchical encyclopaedia which anyone can edit – something which is responsible for the very success of Wikipedia in the first place.

In economic terms, Wikipedia policy is a scarce resource, in that not all priorities can be met simultaneously. For example, giving anonymous editors automatic access to means of editing that allow both productive and vandalistic contributions—such as editing the main page—cannot be simultaneously made technically possible and impossible. For each potential change in policy or new measure adopted, there is a trade-off according to which we must weigh the marginal benefits of satisfying competing priorities. As the relative benefits of increasing counter-vandalism decline (as counter-vandalism becomes more effective), the less weight we ought to accord to arguments to implement changes which aid counter-vandalism at the expense of other priorities.^[2]

The guiding principle of editing Wikipedia is that we are here to make the encyclopaedia useful for readers. Keeping it free from vandalism is only one way among many of contributing to this goal.

If indeed vandalism does not matter, this is only contingently so. Although blatant vandalism is much easier to combat than before, new forms of vandalism are constantly being created,^[3] and subtle vandalism as well as tendentious editing remain major problems. Furthermore, although the decreasing importance of vandalism should give us cause to rethink changing our policies or culture to combat it, it by no means implies that we should be less vigilant in the amount of effort we devote to it. Nor should for a minute diminish our appreciation and respect for vandal-fighters, without whom one of the most successful encyclopaediae in history would quickly become a glorified sandbox.

• Wikipedia:Make articles useful for readers
• Wikipedia:Main Page featured article protection
• Wikipedia:Welcome unregistered editing
• Wikipedia:Concerns about Speedy Deleters