Well, I agree that anyone would be angry in that situation but in the context of the whole movie it definitely does support his character arc of being someone who believes in upholding the law to becoming disillusioned with the system he was fighting for. It was an outburst in a stressful situation, but it had greater meaning. "You're killing us! Yeah, follow your orders!" It's that whole situation that finally leads to him tossing his badge into the river. Now, I'll admit that the pent up anger thing is probably more my interpretation than anything, but I think it's supported by the film because Blake talks about having to hide his anger to be accepted, so when he finally has that outburst after being so reserved for the entire film (despite people calling him a hothead), it felt like the jack finally came out of the box so to speak and we were seeing a different side of him. Now if the scene/character didn't emotionally grab you, fair game.