Wikipedia:Inclusion is not an indicator of notability

A common argument used against the deletion of certain articles is that other articles similar to the one in question exist. Because of the openness of Wikipedia it is nearly impossible to manage the flow of articles. The presence of similar articles does not necessarily validate the existence of other articles, and may instead point to the possibility that those articles also ought to be deleted. Inclusion is not an indicator of validity, notability, or quality because any individual may edit a page. For example, if there are 20 little-known garage bands that have articles on Wikipedia, it is not a valid indicator that any other little-known garage band deserves an article.

Examining Wikipedia policy is more persuasive and practical than citing existing articles. Citing any article which has apparently survived unscathed does not necessarily validate that article's existence. This is due to the fact that Wikipedia is a growing, developing, and ever-changing body of work, and nothing within its realm can be taken for granted.

An editor nominating one article for deletion is under no obligation to search for and nominate related articles of a similar level of notability (though they often do). Inconsistent enforcement of the deletion policy is a problem which is not the responsibility of any single editor. If you think another article is of equal non-notability to one being considered for deletion, you are welcome to nominate that article as well, but please do not disrupt Wikipedia to make a point.

Conversely, non-inclusion is not an indication of non-notability. Since Wikipedia is continuously growing and expanding, new subjects and types of articles get included all the time. To suggest that a particular article is non-notable because no other similar articles exist would stunt the growth of Wikipedia, and do more harm than good.

On the other hand, if a similar article was nominated for deletion in the past, but kept, this does suggest the topic is notable, since notability is one of many factors evaluated when deciding whether to delete an article. However, consider that there may be essential differences between the two topics, or that inclusion standards may have shifted over time, such that the article would not be kept today.

Relatedly, mention of a subject in another article, or inclusion as a list entry in a stand-alone list article, is also not an indicator of notability. The standard – known variously as being encyclopedically relevant, non-trivial, or non-indiscriminate information – is governed by a separate policy and is a much, much lower standard. An article on a musician might mention that her dog, seen frequently with her in public, is named Mr. Fuzzbucket, but this is not grounds for creating the Mr. Fuzzbucket article.

A better argument at WP:AfD
If editors fear that an article is being unfairly nominated for deletion, their arguments will carry more weight if they are framed in the notability guidelines or the relevant deletion precedent.

An alternative view: Sometimes inclusion might indicate an emerging consensus for notability
The participants at AfD and the talk pages of notability guidelines might conceivably be a small minority of editors who are unrepresentative of the community as a whole, in that they are significantly more deletionist than the average editor. If this is the case, creation of articles on a particular type of subject might, in certain cases, indicate notability for that type of subject.

Illustrative example: WP:POLITICIAN tells us that unelected candidates are not necessarily notable. Suppose that a thousand articles about unelected candidates are now created. If they are created by one editor, their creation proves nothing about notability. If they are created by a thousand editors, that might indicate an emerging consensus in favour of the notability of such persons, because of the number of editors who apparently support such notability, assuming that participation at AfD and on guideline talk pages is by a significantly lower number of editors. Presumably we don't want to altogether ignore the views of editors merely because they can't find their way to AfD or guideline talk pages.