system
Given the following post, respond as if you're commenting on Reddit:
human
[ASOIAF] [SPOILERS] How much of what was going to go down at the Red Wedding would the average Frey soldier known of?

(Spoilers for A Storm of Swords and Game of Thrones Season 3). 

So obviously the Red Wedding was planned long in advance between Tywin Lannister, Walder Frey and Roose Bolton. The plan was executed almost perfectly with the massacre in the hall being near simultaneous with the Frey and Bolton soldiers turning on loyal Northern soldiers in the camps. It seems as if every man knew his role. However, the Bolton (and less so they Frey) common soldiers would've fought side by side by their brothers in arms. While Roose Bolton and big man Frey himself are clearly terrible people who would easily give this plan the ok if it benefitted them, would not a single soldier or captain in the massive number of people involved in this plot have had doubts or perhaps even warned someone?
gpt
Same reason Tywin Lannister's men were all OK with gang raping a 14-year-old. Like Tywin, Walder and Roose made sure every one of their men that was present was OK with the massacre. And this is Westeros - it's not like there's a shortage of monsters.