The premise is that you shouldn't be upset with the coaches because other teams lose to inferior teams as well. The problem is I can assure you the fans of those other teams are really annoyed with their coaches when it happens. Nobody, as a fan, should say "oh well. I don't care that my team lost to a really crappy team because other teams will lose to other bad teams".

Since when is fanhood tied to other teams we don't care about and their performance record against bad teams? I care what my team does and when my team lays an egg against a horrible team, I will be mad at the coaches.