I've long wondered if rules against cheating were devised to protect physically powerful people from mentally powerful people. Competition rules generally restrict mental action rather than physical -- although there are exceptions, such as the rule against grabbing a face mask in football. I suppose the purpose of condemning cheaters is that there's a consensus that competing in a certain way is more fun than having a free-for-all, and players decide beforehand which skills are going to be allowed to be used in the given game.
Once winning becomes more important than the enjoyment gained from competing in a certain way, then the game changes from one of cleverly working within the rules to one of deviously breaking the rules without getting caught. If players wanted to follow the rules, then referees wouldn't be necessary; since they are necessary, we can infer that most players want to break the rules and are only constrained by a fear of getting caught. Ergo, even though most players would denounce a discovered cheat, the denouncement would be a show designed to maximize the penalty imposed on their opponent and not based on actual outrage.
The only moral consideration involved with obeying game rules is the supposition that each player has agreed to abide by the rules -- and it's morally incumbent upon a person to keep his agreements. There's nothing inherently immoral about traveling in basketball, unless you've agreed not to. However, since we've already decided that most players are looking for ways to cheat without getting caught, it isn't much of a leap to suggest that the supposition that all the players have agreed to play by the rules is false. If all the players haven't agreed to play by the rules, then it isn't morally abhorrent to break the rules since there's no consensus.
In a sense, then, the mere presence of a referee probably prompts players to break the rules more than they otherwise might. After all, the ref is there to sort things out, and whatever he doesn't see doesn't count as cheating. On the other hand, playing without a ref might incline players to focus more on the competitive fun rather than winning at any socially acceptable cost (such as cheating and not getting caught).
Note that we're talking about game rules here, in which there are no absolute rights and wrongs; the same logic is obviously inapplicable to other moral contexts in which right and wrong are not determined by human consensus.
Montgomery Burns said it well:
Burns: Tell me, Simpson. If an opportunity arose for taking a small shortcut, you wouldn't be adverse to taking it, would you?
Homer: Uhh, not as such.
Burns: Neither would I. I've always felt that there's far too much hysteria these days about so-called cheating.
Homer: Yes, a lot of -- hysteria. [worried look]
Burns: Mm-hmm. If you can take advantage of a situation in some way, it's your duty as an American to do it. Why should the race always be to the swift or the jumble to the quick-witted? Should they be allowed to win merely because of the gifts God gave them? Well, I say cheating is the gift man gives himself!
Homer: Mr. Burns, I insist that we cheat.
-- "Mountain of Madness"