Firstly, this is a brilliant article. I have not read something like that on an internet forum for a long time.
I can fully believe all this in the Roman legions. Those that entered were brutal men, and they were not the warriors of other cultures, for example, the Greeks. These were poor men, commonly from the dregs of society, looking for adventure and promise of land if they survived the 25 years. They did not fight for honor, and they did not fight for Rome. Most soldiers had never seen Rome, and most never did. They were ordered by the rich folk, and in turn, these orders were passed through the alpha males, or the centurions. They did keep order by brutality, as we see with punishments such as Decimation, which was an extremely harsh punishment, not designed to inspire loyalty, but to inspire fear.
The legions did have a brotherhood, but the legions also had everything commonly found in a prison. Many of the men were like convicts in the fact they were brutal, they were all powerful men, and they were dangerous. They were indeed given slack pay, bad hours and a tiring career, and at the end the 'land' they received was commonly in a outlying province, such as Britain. It is understandable that they felt resentment, and it only takes one to set off that spark of resentment. Sure, the officers could usually keep order, but in a legion of 5,000 men, all alpha males, it is only natural that order will fail at some point. Rome channeled these men, and concentrated them into a fighting machine, but even a fighting machine like a legion can not be kept in line for ever like that.
For example, the mutiny before the invasion of Britain was one of fear. The legions heard such incredible rumors that Britain held, such as monsters and beasts, and they decided not to go. This group decided that their pay and what Rome was currently offering them was not enough to invade over the sea. They did not want to die so that Claudius could cement his position in Rome, a city they had never laid eyes on. And they did not want to follow their officers from Rome, who did not care about the men at all, and only wanted to advance their own careers. And eventually what had to happen was that the alpha males who implemented this mutiny were killed. Order was restored, by brutality. The legions then captured Britain.
This system did work, as we can see from the magnitude of the Roman civilization. But it would always spark these outbursts, and these outbursts had to be put down or the system would fail. You must remember that Rome was ruled by a few rich officials, and they commanded through the use of force. And therefore the legions were a mirror of that. The commander and tribunes were the elite, and they used the centurions, men who they could count on to keep the other men in line through their fearsome personalities. And in turn, the men followed this system. But as you state, there is only so much a man can take before he reaches a breaking point. And that is what happens in a legion mutiny.
So in answer to your question, I believe it was the Roman society. Ruled by a small elite, they could not keep the masses in line by themselves. The legions were meant to protect the elites through conquest and policing duties. They were governed by the same system, and so mutinies happened, much like food riot might happen in Rome. They are completely similar in the fact that Roman society worked through controlling the masses, and to do that force was needed. Sure, they could count on respect or loyalty to keep order, but when times get bad, how can you inspire loyalty? Therefore fear was used in Roman society, as it was universal and could be counted on. So the Roman legions followed that system as well.