The practice of deleting anonymous text which is simply an accusation and/or attack on other WikiCitizens?.
This is a somewhat questionable practice, based on the nature of the accusation. Is "You obviously don't know the first thing about the history of operating systems" an ad hominem attack or a warning that the original poster does not know what s/he is talking about?
If the anonymous accusation "You obviously don't know the first thing about the history of operating systems" is followed up with a good history of operating systems, then the accuser is probably correct. But regardless, why not just delete the accusation and let the knowledge stand on its own? Even better, replace the ThreadMode with DocumentMode.