Summary: David (hey I know that guy) wants to show his loyalty to God through his integrity. To that end, he promises is associate and do business only with people of integrity; as king, he also promises to do away with those who cheat.
Response: On the one hand, having no sleaze or corruption in a country would be grand if not unheard of in today's society. On the other hand, the penalty seems a bit excessive, even given how the crime distorts so much about public service and even given that this is David's personal feelings, which he's entitled to. I mean, imprison them, take their position and influence away, root out corruption, but it doesn't have to get that bloody, does it?