This is a bit long and mostly history, so you might want to skip it...
elian wrote:
Second question: Since when is the fact that some user was banned a valid reason (without giving any other reasons) for deleting entire articles?
To expand on Zoe's answer: the question of contributions from banned users came up with the "MIT vandal".
In case you missed that one, he was someone who had been in an edit war on [[woman]] and a couple of other pages. The [[woman]] page was locked for a while to let things calm down. This *really* annoyed him, and he set off on a campaign of random deletions and deliberately inaccurate edits (changing a date or a country to make the article wrong and so on). We had several hours of intense vandalism under numerous IDs. He couldn't be blocked initially because he was logged in each time. He left saying he would be back to carry on, with the stated intention of making Wikipedia unusable (he added this as a comment to his edits).
Anyway. He was banned (obviously!) but returned under different IPs to vandalise again (the same random deletions and inaccurate edits) and, more controversially, to edit some of the articles he was interested in.
Jimbo said: "This is a true simple vandal with a track record. He's banned from wikipedia, and that's that. We must not encourage him by considering each of his edits independently. Anything he writes should be reverted instantly, and his username vaporized as fast as possible."
Whether this also applies to those banned for reasons other than simple vandalism seems less clear.
Regards,
sannse