I mean the whole reason to murder them was to stop a raiding party from stealing Shaolin martial arts and letting their soldiers learn it and become unstoppable compared to the Sung army. WTF kind of reason is this to get all worked up on? There are countless martial arts manuals that they can be stealing, copying, and even buying from many sects and masters where if their soldiers learned it, they would be unstoppable (compared to regular soldiers with no martial arts). Shaolin martial arts actually seem one of the worst as they require a state of mind totally conflicting with a soldiers', and it seems to have extremely slow buildup for an average person. A number of unorthodox martial arts would be much better for an average joe looking for a quick powerup, especially when unorthodox members would be likely to sell martial arts for power and wealth. If they choose to involve themselves in this raid, they'd be committing themselves to likely be stopping hundreds of such raids as the Liao army can likely afford to send many such parties.
It just seems like this was one of those moments where drunk people think every idea is the greatest in the world and has extreme logic behind it. YEAHHHHH LETS STOP THE KHITANS FROM RAIDING SHAOLIN WOOOOO!!!