Wikipedia:Not every IP is a vandal
|This essay contains the advice or opinions of one or more Wikipedia contributors. Essays are not Wikipedia policies or guidelines. Some essays represent widespread norms; others only represent minority viewpoints.|
|This page in a nutshell: Check before you revert an IP's edit, as what may seem like being bold and clever may just be shoving a new user out of Wikipedia editing forever.|
Take a look at this. I don't mean to single any one user out, but this edit revert was not necessary. This was probably reverted because the editor wasn't registered; i.e., they were under an IP address. Of course, most of these are indeed vandals: a quick look at Special:RecentChanges will tell you that. But these edits are usually reverted – and usually without checking what the edit consisted of. What I'm getting at is: Not every IP is a vandal.
When looking for vandalism, many search for red usernames without a second look at the blue ones, assuming that red usernames signify a new vandal or IP to punish. Unfortunately, this is not always the case. This is a good example. Some users don't make userpages: One substantial editor I can think of is Nanonic. He hasn't made a userpage, yet keeps adding to Wikipedia religiously. The IP 126.96.36.199 made over 1,600 constructive edits to the English Wikipedia. Other non-vandal IPs include 188.8.131.52, 184.108.40.206, 220.127.116.11.
On the Scots Wikipedia, there is an IP that constantly helps us out with vandalism and other tasks like translating. He has been there for more than a year without a username and has become colloquially known as 84.135, a shortened form of the IP.
On Wikispecies, the IP 18.104.22.168 constructively contributed over 10,000 legitimate edits and thousands of new articles. The IP only registered simply because he needs to request to become an administrator to deal with vandalism by other IPs.
And probably most prominently and locally, right here on the English Wikipedia, 22.214.171.124 (now known as 126.96.36.199) is likely the best example of an IP editor on Wikipedia. They have been around for years, and had a request for adminship. An inspirational user, and one without an account.
Check before you revert
So, to finish, please oh please check before you revert, as what may seem like being bold and clever may just be shoving a new user out of Wikipedia editing forever.