I'm not saying it's right, just that it's understandable. To use a software analogy it would be like if for your job you were forced to help make a website for anti-software developers who hate you and your profession, and you are treated poorly while trying to do your job. That environment is not going to cultivate craftsmanship to say the least. The right thing to do is to dutifully and professionally execute your tasks, but in reality people have emotions and some software engineers in that position might sabotage the project out of spite.
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.