Wikipedia:Why Manual of Style discussions are so awful

Discussions about what Wikipedia:Manual of Style and its sub-guidelines (hereafter "MoS") should say, or how/whether something they says should be applied to a particular topic, often turn into verbal brawls characterized by assertions without evidence, viewpoint-pushing, original "research", undue weight given to one or another primary sources (if any are provided at all), sometimes even promotion of fringey notions, all toppped off with incivility that increases the longer the discussion continues. This is all clearly contrary to Wikipedia policies. So what is going on?

Despite Wikipedians' inculcated habits of turning to reliable sources in a duly-balanced manner to ensure that any claim they make is verifiable, in MoS-related discussions the norm seems to be do no research at all and just pop off with an opinion (usually relying on prescriptivist notions about what is "proper", "right", "correct", "true", "required", "standard", etc., etc. – claims no linguist or other scholar of the language would ever agree with in most cases). Even in the rare instance a drive-by commenter does look for any sourcing at all, they usually cherrypick whatever style guide or other source agrees with their viewpoint and preference, and suppress any mention of ones that do not (and are apt to attack them if they are mentioned by someone else).