This post assumes that a meaningful amount of defed instances are caused by simple lack of agreement. Often, it's an orthogonal matter - it boils down to instance A actually understanding something about the userbase of instance B and saying "I'm not dealing with this shit, it'll make the instance worse for its own users". For example: the typical user of B might be disingenuous, or preach immoral prescriptions, behave like a chimp, or be a bloody stupid piece of trash that should've stayed in Reddit to avoid smearing its stupidity everywhere here.

Are instance admins too eager to pull the trigger for defed? Perhaps, in some cases; specially because it handles groups of users instead of individuals. But those cases are better addressed through actual examples, not through a meme talking on generic grounds.