This is probably going to be an unpopular opinion but here it is. We have all been sold on the idea that being a cop is a really really dangerous job. Statistically, it doesn't even make the top 20 most dangerous jobs in the US and it comes in significantly behind traveling salesman, truck driver, and garbage collector. Now, I'm not saying it isn't dangerous, but it's not the most dangerous, and in the end it's all relative. If you ask the average person and probably many cops, I'm guessing they'd all say it's in at least the top 5. Well, it isn't but that hasn't stopped us from turning local police, whose motto is, "To Protect and Serve", into a paramilitary-like force.
There is a ton of video footage out there of a group of police who enter into almost every situation already revved up, adrenaline already pumping, and the other cops around them and society as a whole reinforces the idea that this job is so dangerous that being vigilant isn't enough, and instead, you must be domineering or you will get shot and die. This then extends to the idea that too many cops believe they deserve "respect", not just in the form of someone being compliant, but people must also show SUBMISSION. As the person stopped, you must go out of your way to make them feel like you understand that they are in control and if you do not, you are a threat and a problem, and many cops will escalate the situation to make you submit.
This is a problem in this country even if it is a minority of cops. I've been pulled over several times and no one has attempted to dominate me in the situation. A couple questions, I submitted my paper work, and I was on my way. So, I know there are cops out there who can remain cool, calm, and collected but clearly we also have a population of cops looking for a fight. It's a difficult job where you see the worst possible side of people and it can be very dangerous, but you are there to serve the community, and that takes a special kind of personality to be able to manage the job.