Wikipedia:Wikipedia is not about us
If you're viewing this page, Wikipedia doesn't exist for your benefit.
Well, it does, assuming that you're a human. But it's also written for the other >99.9% of users—the ones who don't visit the "MediaWiki" namespace, don't know how to modify their CSS, and probably don't even edit.
Before arguing that we need to do something a certain way to remain neutral in an edit war, avoid offending the members of a WikiProject, or ensure compatibility with a custom script that your friends and you use, please consider how this course of action affects the aforementioned >99.9%. You know, the encyclopedia's readers.