Intimidation is a major aspect of it. To quote from Lois McMaster Bujold's Shards of Honor
"I have an aversion to stunners, in that sort of situation," he said slowly. "Nobody hesitates to rush one, and if there are enough of them they can always get it away from you in the end. I've seen men killed, relying on stunners, who could have walked right through with a disruptor or plasma arc. A disruptor has real authority."
"On the other hand, nobody hesitates to fire a stunner," said Cordelia suggestively. "And it gives you a margin for error."
"What, would you hesitate to fire a disruptor?"
"Yes. I might as well not have it at all."
"Ah."
Curiosity prodded her, mulling on his words. "How in the world did they kill him with a stunner, the man you saw?"
"They didn't kill him with the stunner. After they took it away from him they kicked him to death."
Put people in a situation where they know they'll survive as long as at least one of their members gets through and they'll be willing to charge the person with a weapon. Give them a situation where each individual is risking their life and few will be bold enough.
