I'll go out on a limb, and say that the existence of police unions is not the most important factor behind police brutality, and the killing of people of colour by police, in the US.
As one example, look at training and employment. It takes three years to become a police officer in Germany or France. Once you are one, you are employed for life (after a probation period). A lot of the training is focused on legal work, de-escalation and so on. Is there still excesive use of force? Yes. Still racial profiling and protection of your felllow officers? Yes and yes. Do you have to be affraid of police? No. Does police have to be afraid of the population? No. Are there exceptions to this? Yes, as always.
Anohter, very big difference, between France germany and the US is, that in france there are two police organisations (Police and Gendarmerie), in Germany a federal one and one per state. All are follwing the same regulations with only minor differences between the states in germany, and differences in area of responsibility. Compare that to the US with city-based police departments, sherrifs departments, sate police and so on. The former makes it easier to implement common standards, the latter makes it harder.
> I'll go out on a limb, and say that the existence of police unions is not the most important factor behind police brutality, and the killing of people of colour by police, in the US.
Hard to say if it is the most important but it is a pretty important factor. See https://www.joincampaignzero.org/ for all research that indicates the unions are a key stumbling block.
That is true. On a meta level, that is kind of what a police union should protect interests of the police force. Shows how this, be it unions or any other association, can backfire.
Witness how many times the policeman who killed George Floyd had complaints against him and was protected by his union.