ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
From previous post:
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.
What would the incentive to become a traitor before the battle of Chapter 33 be? Before Quirrell added the ability to switch sides, you'd just be helping your army (which you've already developed a bond with in the first battle), and therefore yourself, lose. I'd expect this to strongly outweigh the fun of being a spy.
I just Googled for "airsoft betrayal" and "paintball betrayal." I found no stories of similar events in either sport. (I did however find one person hypothetically talking about betrayal in laser tag, even though many/most systems ignore friendly fire.)
"Team killing" is annoyingly common in online FPS games...