That's the problem with wearing that outfit, though. Why would anyone give you the benefit of the doubt that you simply were looking to have a discussion? How long did it take before the cop started issuing commands? Who would assume that this person's profession was irrelevant, and that it was just a guy making requests?
The vet escalated things, and if he were dealing with a normal person, it would have been pretty indefensible for him to actually use force when, and in the way, that he did before trying to just leave the situation. However, cops don't typically make requests, and then leave people alone when they don't comply. Again, it's sad, but this is bound to happen when one treats people this way (or affiliates with groups that are known to do so).
I'm not saying that the vet was a harmless person, or that I would have made the choices he did.. However, there are consequences to being affiliated with dangerous thugs. In a free society, those who threatened people into pulling over, etc., and those who were so quick to fire at them, would likely not live very long.