I don't think it's an overreaction at all to be upset at the selfishness of this mistake. I can only speak for myself here, but I absolutely feel sick that he's done this after all the team has done on his behalf.
As for standing up for teammates, I'd expect nothing more from them. I'm glad about that, because Walter will only be left with feeling worse about it, knowing what it causes for the team.
I am beyond disappointed, but mostly because of the nature of this needless stupidity. Leave no doubt, indeed.