Killing yourself, or jumping on the grenade as DR put it, is certainly an option in the second scenario. So yes, personally volunteering to risk the freezing waters yourself is a valid answer. However, I was actually the most interested in seeing if people could find the logical inconsistencies in the lifeboat situation, because it was precisely those loopholes that I felt could be exploited to save everyone without having to get bent out of shape about who has to die.
As it has been pointed out, there's a big freaking iceberg nearby. One of the theories about how the Titanic could have been saved involves hitching the ship to the iceberg itself, because obviously the iceberg floats. Moving people onto the iceberg rather than risking the lifeboat could be a viable way to save lives in this case. Secondly, it would be pretty stupid to deliberately overload the lifeboats in the first place. Any cruise ship is going to have plenty of other materials that float, such as wood furnishings, and those would be better than nothing. Third, I think it's a rule nowadays that large ships must have enough lifeboats to accommodate all the passengers, although I haven't checked into this.
Personally I never would have gotten onto the lifeboat in the first place if I knew one more person would cause it to capsize. It'd be the fault of the last person to get on board, regardless of what shape they're in. Of course, a stupid cruise in iceberg-infested waters is not my idea of a fun vacation, so I wouldn't be in that situation anyway.