Not so sure that it's as innocuous as one might think. There are plenty of documented cases of entire groups getting sick from swimming in a pond/swimming pool where a couple of those swimmers dropped a mud monkey.
Look at the pfiesteria blooms (AKA red tide), that have decimated fish populations along the entire eastern seaboard and even as far as into the northern gulf of Mexico. These so called red tides result from the massive dumping of hog poop in the Atlantic from North Carolina, the largest pork producing state in the country. The entire bloom is not a direct result of the poop, but it's the poop that give it life, before it quickly takes on a life of it's own and robs the oxygen and sunlight from near shore ocean waters. These blooms kill fish or drive them away from their native waters to escape them so they are not just damaging the environment, they also hurt the economy of places that depend on sport fishing as an engine for the local economy. I know a few NW Florida guides who have suffered greatly from these blooms. No fish means no anglers, means no guides, hotels, restaurants, etc, making money. If you do happen catch fish around these blooms, they will have angry open bloody lesions on them, and if you are careless in handing them you too can experience the joy of a pfiesteria infection.
Not saying that cruise ships dump near that amount of waste, but it's more about time of year and water temps than how much poop is present. Once pfiesteria gets a toe hold, it's all over but the shouting as it spreads at a rapid rate, gobbling up all the micro nutrients and oxygen while blocking sunlight.
As for the OP's concern about stopping cruise ships from dumping doodoo, based on the info provided my BS meter was pegged at maximum. It sounds like a total scam to get people to send money.