A civil war because an 11 year old girl didn't lose fifty house points as well as the detention she got as punishment for being attacked by 44 students? When, mind you, Lucious's son had been backing Hermione himself? That's just absolutely absurd.
The wizarding community in Magical Britain is pretty close to civil war in general. The community is small so small scale results can have larger impact, and Hogwarts is the only magic school in Britain so people pay more attention. Moreover, the wizarding world has a lot of values based on medieval ideas. In Roman times people fought wars over chariot team winners. In modern times that's translated into wars about football.
The idea that discipline issues could be a significant enough dispute to push them over the brink is not implausible.
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: