Not sure what an honest Ponzi scheme is, but obviously not only would a contract for a Ponzi scheme be unenforceable, but Ponzi schemes are also criminal.

I'll give real world examples that go both ways:

1. Parking garage tickets: they include tiny little print saying the garage won't be liable for lost or stolen items from your car. Generally if your car is broken into those will be enforceable and the garage won't be liable.

2. Sky diving contract: include tiny little print that says if I die as a result of the companies negligence, they won't be liable and/or I waive my right to sue. Unenforceable, you can't waive negligence. (think about a skydiving school forgetting to pack a chute, someone dying, the family suing and losing, because of a defense that the deceased waived out negligence in the contract).

Lets look at a potential negligence claim against the creators of the DAO code.

1. By creating and soliciting investment for the DAO did its creators the investors a duty? If yes go on;

2. By creating code that allowed ~$40M of investors funds to be taken, was their a breach of that duty? if yes, go on

3. Did the substandard code result in damages to the investors? if yes go on

4. Can the investors prove monetary loss? if yes, you have a good civil claim for negligence against the creators of the DAO for the damages.