I think the concept of a 72 hour contest promotes an unhealthy habit of sitting on the computer for long periods of time, getting little sleep, and has an impact on participant by requiring a long weekend and flow effect on the following week.
You are truely and absolutely right. Marathons are technically bad for peoples health because it puts a lot of stress on them, but yet, thats an olympic sport! I make sure to tell people through out the event that their health comes first and that they need to make sure they stay healthy, not necessarily finish their map. (I'm looking at you, Crash)