Niall,
Your expectations of your fellow golfers are rather ideal, romantic even. We are talking about the same guys and gals who don't fix their ball marks on the greens, sand or replace divots, rake bunkers, dispose of trash appropriately, etc. The % of this type may not be large, but their effects are noticeable.
The rules are there to facilitate fair play, but they do not guarantee it. I disagree with Erik that the rules are simple and easy to understand. They might be for John or Erik who made/make a living in the game and had/have some responsibilities in tournament administration. They are certainly not for me and I've read the book many times over.
There are any number of possible reasons why Lexi fanned the natives before hitting her shot. If we had the ability to put her through an FBI lie detector test, I would place a good sum of money that cheating was not her motive. Like so many golfers, a number from this site whom I've played with, some have less than proper habits around the ball. I think that this is Lexi's problem, one that she needs to be counseled on.
As to other sports, I played basketball and baseball in high school where we were shown how to take advantage of the rules in all sorts of nefarious ways. It was expected that a player would employ these tactics, and if he didn't get called on it from time to time, he just wasn't being aggressive enough.
I've seen some outright cheating in club tournaments on two or three occasions, but any number of rules violations that I am sure were the result of ignorance or carelessness. The rules and the spirit behind them require that we protect the field from such violations. I wonder how many of us are willing to take the heat for calling a penalty on another competitor. I've refused to sign a scorecard on two occasions involving blatant, intentional violations. It didn't make me very popular with the pro as he had to resolve the matter, which he did by signing the card himself when a DQ was the proper call. It is called the path of least resistance/conflict avoidance. We do like our +1s!