Modular Morals

When I was running a Tomb of Horrors, one of my players was quick to reassure me that he hadn’t played the adventure, and that (apart from the leering green devil face) he knew nothing of the rest of the adventure. But it was a thirty-five year old adventure. Even if it hadn’t been played, there was lots of time to have read it. If this had been a similarly old movie we were watching, it would have been well beyond the statute of limitations of spoilers. Heck, for many people it’s fair game to spoil away within a couple weekends of a film’s release (as someone with a young child who can’t get sitting easily, I say “BOOO!”), so why is this module off limits for reading? Why did it have to be played?