No, the core premise of a union is to represent the interests of its members. You've confused a union with global communism, and delegimitized the ones that don't serve your interests instead.

For an extremely salient example, the purpose of coal miners' unions is to serve coal miners. The interests of coal miners don't necessarily align with everyone else's interests, and if the the interests of their union did, it would be a bad union.

If police are racist, police unions are either racist or not representative. The purpose of unions isn't to serve the purposes of upper middle-class liberal arts majors. You don't steer workers through their union, that's evil. If you want coal miners to prioritize the climate, or police to prioritize civil rights, you have to do it the traditional way - by convincing them. You might have to convince them to quit.

The idea that the police don't deserve a union because police unions would support your enemy is repulsive. Change the laws, maybe you wouldn't have to hire scum to enforce them.