She made an error, and it was somewhat serious. That’s not the issue. The issue was the media’s (and some of the public’s) treatment of a false equivalence between:
a) Clinton being sloppy with a mail client because their IT setup blocked their work in a way that’s really common among Fed. employees, if widely prosecuted would nail a significant percentage of Fed. employees with charges, which Trump’s advisor Gen. Flynn also engaged in and wasn’t prosecuted for, and which once Trump won he acknowledged he hyperbolized and lied about the seriousness of
vs.
b) a person literally engaging in mass scale targeted fraud exploiting the hopes of the poor and struggling, paying for defense lawyers of mafioso bosses who’ve committed serious crimes, being hit with housing discrimination suits for refusing to rent to minorities, bragging about sexually assaulting women, calling Mexicans murderers and rapists, calling for Muslim registries and wide scale persecution of various minorities, incessantly, egregiously, selfishly lying about things that were obvious in your face obnoxious lies, and a litany of other mind-bogglingly vain, horrible, ugly, mean-spirited behaviors.
a) was investigated by the FBI who didn’t press charges, made the front page of the Times dozens of times, was chatted about incessantly on cable news, and while not a trivial issue, was treated as something many orders of magnitude more serious than it was in the interest of “balance” by our worthless corporate media, and which fucking Comey illegally dragged out as an October Surprise, swinging the election to Trump.
So it’s not that the email business wasn’t an issue (there were a set of problems there), it’s that the severity of the issue, which was basically someone occasionally being a bit lazy and sloppy with an email client when they shouldn’t have, was treated as something morally equivalent to committing fraud to deliberately exploit the poor and desperate or intentionally whipping up the rage of the white working class against Muslims, African-American and hispanics with the intent of fomenting blame and hatred against that minority for personal gain.