Another way of putting it, Rapaire, is that Yarrow's "Greenwood" song is basically saying,
"He who would lie, cheat, and steal when the stakes are low is even more likely to do so when the stakes are high."   It's a matter of degree of need or temptation, not a question of whether values and codes transfer from one area of conduct to another.   There are thieves and murderers who would never "rat on" one of their own; that would violate their own code, whereas stealing and killing are violating someone else's.