Let's take a look at the collated reports from the Thurston County Sheriff's deputies, specifically the second one, the lieutenant's report (see page 11 of the .pdf file):

I tried to calm the crowd and assure the ones closest to me that she [TESC Police Services Officer MEYERS] would only be taking him [the arrestee] to the campus station to be processed and would most likely be released. This did not diminish the crowd's displeasure with the action and they began to press in closer, shouting louder and still being profane towards us.
[...]
I then asked officer Meyer [sic] if she would just ID the suspect and release him for later charging. Officer Meyer agreed to this [...] During the time that the decision was made to release the suspect, we were trying to let the crowd know what the plan was. Officer Meyer also tried to tell them but was shouted down.
Some were aware and we tried to get them to spread the word. As officer Meyer was trying to get ID, we began to get items thrown at us. Both Sgt. [redacted] and myself had members of the crowd grab our guns and try to pull them from behind. [...] Both Sgt. [redacted] and myself began to feel very unsafe as the crowd in our vicinity kept approaching us very closely and were hampering officer Meyer's efforts to ID and release the suspect. I then began being struck by objects thrown from the crowd, some of these were hard enough to be slightly painful. We repeatedly told the crowd to back off and get away from us and the patrol car with no compliance.
Others in the crowd tried to get the throwing to stop but it continued, as the mood became even more unruly, with the people in the crowd becoming more aggressive.
I had requested additional units earlier and they had been standing by as we had made our initial efforts to deescalate the situation. With our safety becoming more and more in question, I requested that the additional units try and move the crowd back from us and the patrol car.
Olympia Officers entered the scene and met with immediate resistance. They deployed pepper spray [...]

Emphases in italics mine. It's worth noting that the salient points in the lieutenant's report are corroborated by the reports of TESC officer Meyers, other members of TCSO and at least one member of OPD. To recap, these salient points are that the sheriff's deputies next to officer Meyers' car, as well as officer Meyers herself, made repeated attempts to de-escalate the situation; that these attempts were unsuccssful; that the TCSO lieutenant became afraid for the safety of himself and his fellow officers; that the OPD personnel attempted to force a gap through the crowd only after the TCSO lieutenant had requested them to do so; and that the OPD personnel resorted to force only after they encountered resistance. Yes, they did so with extreme rapidity, but as a response to a reasonable belief that the physical well-being of fellow officers was in jeopardy. Unless pretty much all the police officers, from all agencies involved, are lying through their teeth and have colluded. But unless and until I see some evidence of that, I'm unwilling to accept that explanation without question.

It's worth noting in this regard the context in which the first group of TCSO deputies were summoned to the scene. According to officer Meyers, she had arrested the suspect on the basis of a complaint made by volunteer members of event security, who pointed out the suspect to her. On the basis of the probable cause thus provided, she arrested the suspect, andas she was in the process of escorting him to her vehicle (with the intent of taking him to the TESC Police Services office to get his side of the story), she was confronted, first in the foyer of the CRC and subsequently at her patrol car (parked in front of the CRC) by various protestors, who insisted the arrest she was making was a illegitimate. In both instances, officer Meyers attempted to explain that she had been given probable cause to arrest the suspect, based on the information given her by the volunteer members of event security, and that if the protestors had information contradicting that probable cause, she would gladly take names and telephone numbers so that she could contact these people at the earliest opportunity to get their input. Being unwilling to leave the suspect handcuffed in the back of her patrol car, officer Meyers called for assistance for administrative purposes; the plan being to leave the TCSO deputies outside the CRC to take statements from anyone willing to come forward in the suspect's defense, while she would take the suspect to the TESC Police Services office in Sem. I. This she attempted to the best of her ability to communicate to the gathering crowd, but they were evidently not receptive, and when she tried to drive away, they blocked and surrounded her vehicle. Several of the TCSO's deputies immediately positioned themselves next to officer Meyers' patrol car, and that is more or less where the excerpts quoted above begin. I might note that in the intervening period since the riot, the informal complaints about the conduct of both officer Meyers and the TCSO have dissipated, and the focus has shifted to the response of the Oly PD personnel present. Indeed, the only formal complaint lodged has been directed at Oly PD, not TESC Police Services or the Thurston County Sheriff's Office. But according to both officer Meyers and the TCSO deputies, Oly PD arrived on the scene in response to their requests for assistance, and entered into direct physical confrontation with the protestors as a result of the TCSO lieutenant's request to be, well, be rescued.

Quoth Rob:
"I don't think criticizing the 'mob' gets us anywhere, we can't change the behaviors of crowds, we can only hope to avoid letting situations escalate to the point they did that night."

All the available evidence indicates that repeated attempts were made by the law enforcement personnel involved to de-escalate the situation prior to OPD becoming involved and resorting to force. Unfortunately, the majority of the protestors were not receptive to these attempts. Arguably, with the benefit of hindsight, the one thing that would have been most effective in preventing this situation from escalating would have been for officer Meyers to have ignored the protestors from the start, and to have bundled the suspect into her vehicle and whisked him away to Sem. I before a sizeable crowd had the opportunity to gather. I cannot come up with a plausible explanation why she did not do so (though I'm open to suggestions) except the one she proffered, namely that she wanted gather any available information that would have benefited the suspect (i.e. she was trying to be fair to the guy).

Moreover, I find the notion that "we can't change the behavior of crowds" to be disputable. Crowds are composed of individuals, and those individuals have a choice to become, and remain, part of that crowd. But let's suppose for the sake the of argument that you're right, and that indeed "we can't change the behavior of crowds"; where does that leave us? Evidently, crowds cannot be reasoned with, so that would appear to leave us with two options.

The first is to attempt de-escalation in the short term by acceding to each and every one of crowd's demands, no matter how unreasonable those demands might be. In other words, submitting to mob rule. Aside from the fact that this option strikes me as highly distasteful, it is also by no means guaranteed--or even likely--to be effective. Mobs are essentially bullies, and anyone who's encountered a bully in the schoolyard knows (or damn well should know) that when bullies succeed in getting what they want by bullying, the only effect is to encourage them to persist in their tactic of bullying, since it has proven effective in the past.

The second option is to come down hard and fast on any mass gathering, and nip it in the bud before it gets the chance to turn into a violent mob. No need to worry about the Constitution, because if "we can't change the behavior of crowds," there can be no such thing as "peaceable assembly"; by its very nature, the question whether any given crowd will turn into a violent mob if it doesn't get what it wants (and likely even if it does) is a matter of "when," not "if." Clearly then, the most effective way to keep the peace and protect the public (which is what you were advocating earlier as the appropriate role of the police, Rob) is to impose a police state in which any gathering is dispersed with whatever force necessary lest it inevitably become a violent mob.

Are you sure either of those options is what you had in mind? If a sufficently large group of religious conservatives descends on the state capitol demanding the immediate outlawing of abortion in the state, the immediate installation of Tim Eyman as governor-for-life, and the deployment of every police force in the state to patrol neighborhoods on Sunday mornings and consign to internment camps anyone caught not attending a Protestant religious service, should we give them their way rather than (horrors!) escalate the situation? Or should we send in every cop in the county (WSP included) in full riot gear, give them one (and only one) chance to disperse voluntarily, and let anyone who refuses take their lumps?