I has something to do with parents not unlike yourself.... Outbreaks of illness happen on ship just like they do ashore however the ones on ships draw a complete different qualitiy of bad publicitiy. Over and above that it is not the ship or cruiselines making those requirement but rather the USPH Service and that for good reason!
Imagine if you precious little one had caught something nasty in the water because 100 or so little other ones "used" the pool too during the day. Passed experience tells us most passengers don't even wait for dry land to either call a laywer or the press.
While I don't think anyone here cannot understand your dilemma most of us feel the rules are there for a good reason and should not be bend or broken.