Well "understandable" sounds dangerously close to acceptable. Because it's foreseeable departments need to be extra judicious in which officers they send into emotionally charged situations, officers lacking self-control are going to do the country more harm than good in protest situations.
Indeed. I think it's important to humanize the police officers and acknowledge that they are people with emotions too though. Protestors can get angry and smash/burn stuff, police can get angry and arrest people and disperse crowds. People are people, and this situation is particularly tricky because the opposing parties do not like each other. In an ideal world only the cream of the crop would be sent to police these protests, but I would wager most police departments are understaffed and have to make do.