Are you confusing Customs with the TSA? In general, customs agents are much better trained and there is a lot of former military. TSA on the other hand is as you a low requirement job as you described.
No. I'm talking about the border guards who check passports when flying back into the country. The one I talked to did not understand the concept of dual citizenship and insisted that I get rid of my non-US passport as soon as I entered because it is illegal. This is after failing to find my stamp in my US passport that had all of three stamps in it and trying to claim that I didn't have one! Talk about stupid! This borders on retardation! I assume this is the norm and the other concepts I mentioned are also beyond their meager understanding simply because this guy was so stupid that if he made it through the hiring process, plenty of other idiots have too. Hell, compared to this, the TSA employees are courteous and generally at least do their job properly.