Then add in the reality that people choose to become cops instead of accountants because being an accountant never offers the opportunity to physically impose your will on others. People who want to avoid confrontational situations don't become cops. Cops are more inclined toward welcoming opportunities to physically dominate anyone who questions their authority.
We need people who are comfortable asserting their authority in some situations; we need cops. I respect them and their service. But with authority comes responsibility and accountability and our society has not been following through on drawing those lines. We need to recognize the tendency you refer to and guard against its expression as a power trip not a regrettable occasional necessity.
These guys should not have had the authority for those actions. Their boss says they didn’t and he will be dealing with it. They were under trained for their duties and the passenger paid the price.
United should not have called in cops for an administrative problem. They bear culpability. The crew wanted to accommodate the other airline’s flight crew. But they also lacked the training about what they could and couldn’t do legally to seat those extra flight crew members. The passenger paid the price.
What irks me is people saying the passenger deserved what he got because he didn’t just give up his rights and disappear. He even made noise and made other people uncomfortable by not letting the airline personnel ruin his plans and illegally deny him passage.