Additionally, monitoring can also be exonerating if you are confident in the justice system, so I don't buy this idea that cops are uniformly against monitoring.
My point is that police officers, like you, find having someone staring over their shoulder while they work uncomfortable. So the fact that they don't like it and tend to oppose it doesn't mean they're inherently desiring to be corrupt or violent or bad cops.
And yes, it's definitely true that police are regularly accused of lying, and can find appealing having recorded proof of their interactions. There's a lot of extra rules and regs around body cams and when they have to be recorded, and how they can be used by the department that can make the issue cloudier.
But that fact is the seed that causes such corruption.