"Are we sure we are just looking at the deterrent angle or do progressives go in for outright revenge?"
I think this is an important question--which is why I'm addressing it as a root-level comment rather than a personal response.
I don't think this is about revenge. If the woman in this case had seized on some opportunity in the time since the assault to inflict violence on Brock out of revenge, we might feel some sympathy for her actions, but as a society, we would still consider her actions criminal and though we might feel a tug of reluctance, we would still call for her prosecution. But this is also not about deterrent, or at least, not principally that. This is about justice.
Justice is the way societies attempt to redress failures of moral restraint. It is about showing that the collective many is stronger than any individual oppressor, it is the way we reassure ourselves that society will wield that power on our behalf if any of us are wronged, and it is about avenging the wrong done to a victim. And despite the similarity of the words, to avenge a wrong is something quite different than seeking revenge for a wrong. To avenge a wrong is to try to set the scales right to the best of our limited abilities. It is a penalty for breaking the social contract. and it only applies to the degree such a breakage can be established to be fully deliberate and voluntary. In effect, it respects the full personhood of the offender, because we would not apply the full punishment in cases of diminished capacity. Revenge, on the other hand, is giving vent to the desire to inflict deserved pain on an object of hate, or more specifically, to derive enjoyment from said infliction of pain. As such, the target of revenge is demoted to less than human status, and the target simply becomes a means to gratification through the suffering inflicted on it.
In this particular case, we asked a lot of the victim. She may not have liked the presumption of innocence being applied here, but as a society we require it in all cases. She may not have liked having to face the accused, and to be put through the indignity of interrogation, but we require it to reduce the chances of an unjust verdict. But after she did her part, and the accused was convicted by a jury which unanimously felt he was guilty beyond reasonable doubt on multiple felony counts, he got a six month sentence, possibly out in as little as three--not even a major fraction of the duration of the ordeal the victim went through to arrive at this point. We routinely see harsher sentences handed out for misdemeanor offenses. As a society, that really doesn't feel like the wrong that was done to her was avenged. And when our justice system fails any one of us that badly, it fails as the protector of last resort for the social contract, and in so doing, it fails all of us.
I would even argue that it failed Brock. One of the reasons we have a justice system is as a surrogate to displace and suppress the impulses for frontier justice, vigilantism, and mob retribution which would otherwise tend to proliferate and escalate. Whatever Brock thinks about his sentence, the rest of society sees it as a gross miscarriage of justice. If he'd received a punishment that fit the crime, he would not now be the focus of national outrage, and he'd have been able to slip into relative anonymity and obscurity after serving his time. As it is, the brief time that he spends in prison will be the easy part compared to what comes after. He's going to be a hounded pariah, and thanks to the internet, her witness statement will follow him around wherever he goes until he finds some way to hide or live in exile. --or until he meets up with someone whose impulse for vigilante justice was not sufficiently assuaged by this execrable sentence.