Some of them do like killing. Clearly Chauvin is a huge jerk. Some of them are also scared for their lives and react in fear. The US isn't Canada. Everyone has a gun down there, police are shot more than police shoot civilians, and there's a lot more of us for them to shoot than there are cops for us shoot.
I don't think that's true. In 2019 there were 139 police deaths in the line of duty from all causes (including cancer and car accidents). There were more than 1,000 fatal shootings of civilians by police that same year.
Anyway, the problem is cops are trained to be afraid for their lives at all times, which leads them to react as if they are in danger even when they are not.