Continuing with the theme...
...that cops are a bad lot, this kind of thing scares me.
I'd like to think it's the exception, but I doubt it.
I'm not sure what the solution is, tho. Basically you've got people doing a tough, often thankless job. They're trained (officially, and by experience) to take control, to maintain order, to boss people around. Controlling the situation is often enough an issue of officer safety that they eventually come to feel threatened by *any* situation where they're not in total control.
So when people (who most likely never done the job and don't know what all the issues are) butt in or don't cooperate -- even in a fairly innocuous way -- cops tend to get their knickers in a serious twist*. And it has nothing to do with whether the buttinskis are right or not.
Bottom line, tho -- if you're going to do that job, you need to exercise discretion. And if you've lost your ability to make good judgements about the law and use of force, it's time to look for another career...
*(see previous post)