Humans are also very good on disagreeing on a fundamental level about what is and isn't unethical in general, before even considering rationalizing their own behavior.

But my point is, ethics is not a very strong thing, and alone it doesn't stand much chance against free money lying on the table.

(What I think people miss is that moral behaviour has to be actively maintained in people, otherwise it slowly erodes. This concept goes against the zeitgeist of contemporary western societies though, because it implies there is a standard to hold oneself to.)

The zeitgeist of modern western societies very strongly holds that there is a standard to hold oneself to (it rejects some elements that used to be commonly held to be part of the consensus standard, and adds some that were not, and people who still hold to the rejected elements often portray the new reality as "no standard", when its really just that the dominant standard is now different from their preferences.)