This is far from being an urban myth as it is standard practice in many gangs, and has been throughout history. Those gangs that are based on long histories within ethnic groups have such traditions. This is because humans have been corrupted to be warlike, and this is a significant part of human history, whether engaged in through gangs within a larger group of people belonging within a region or a formal nation, or from a loyalty to one’s tribe that might see another tribe as an enemy and command loyalty of fellow tribe members and a proof of such loyalty as a test of manhood, for example. In more primitive eras, the taking of the human life of those outside one’s tribe was commonly done as a rite of passage, but the practice still exists today, particularly among gang members and organized crime in many parts of the world.
An even larger and often unrecognized example is the oath taken by members of the military to serve their nation no matter what, no matter what they might be called upon to do. Even though most large nations with militaries have formal rules of engagement and there are international laws about the conduct of warfare that most armies will at least attempt to follow, about what is fair, what is considered a war crime, things like unnecessarily killing and targeting civilians to make them suffer, and so forth. But this is a slippery slope, and here again this speaks to the fact that such oaths are frequently an attempt to make someone do something they might not otherwise do. This works both ways—it might provide implied pressure to outperform, to rise to the occasion and be a better person in service to the intention behind their oath they take; but it could also be more an oath that serves the state, in effect, obtaining a promise of loyalty in advance during a calm period without the oath taker realizing all they might be drawn into that will compromise their morality in order to keep their oath. And in the case of the military, will involve much non-divine conduct with great karmic complications and consequences for their future that will bring harm to them as a magnified consequence to the harm they do to others in service to their oath in being a party to war.
Because of the corruption in your world, all human institutions are corrupt, so all taking oaths in service to the workings of those institutions will involve them in the corruption, and they may be blind to the reality of this because of the manipulation done universally to make people complacent and a party to many things seen as “normal” but not truly so. This is another aspect of oath taking and its problems.