The argument isn't stupid. It's actually an ad hominem. I wouldn't normally support ad hominem arguments, but in this case it's not just attacking the credibility of the other party. It's attacking the credibility of all the party shills jumping on the "Clinton is evil" bandwagon. It's arguing against certain readers in particular for being OK with it when their side did it but not OK with it now. Myself, I don't even remember this Bush "scandal".
If you thought Bush was bad and you think this is bad, that's fine. If you don't care about either, that's OK too. If you only care about one and not the other, that's hypocritical. Let's not talk hypotheticals or generalizations. Cahuenga wasn't picking sides; s/he was mainly pointing out that it's too late to worry about the other side doing it once it's OK because they already have. Nobody should be but can we stop acting so surprised and outraged that it did? Focus on the future in which Clinton's emails are unprecedentedly available to the public (not just by FOIA or subpoena like normal) and she doesn't do this anymore. I'd like to think that future includes nobody doing it again but no amount of fake outrage is going to make that happen anyway.
And if your outrage is genuine, well power to you but you are in a vanishingly small minority lost in a sea of party shills ready to attack Clinton for anything and everything