Re: Composting Toilets vs. Holding Tank
I don't think it is a no brainer at all.
Wet plumbing systems are complicated, and sometimes messy. Also, as mentioned just a post or two up, pump outs often close in the cold seasons (and too often just seem to break and be out of service for extended periods). It has also been quite well reported that heavy rains frequently cause an overflow of the treatment plants (often discussed in other waste threads) dumping large quantities of untreated sewage into public waters. Plus, as noted in your summary above, a large percentage of soiled 'naps' are already heading into the landfill, and that kind of thing should be planned for. Your summary also mentions that the general assumption is that the waste is quickly deactivated. Besides, unless you are going to stop all diapers, tampons (I've seen signs in MENS rooms warning not to dump tampons in the toilet), dog waste, kitty litter, baby wipes (don't flush them, either) and everything else from making it into the landfill, I would think stopping every boat with a composting head from trashing their waste (maybe three gallons worth of partially composted material every few months) is extremely unlikely to produce any kind of measurable result. I suspect that if we all started burying our poop in shallow holes, there would be an awful lot of shallow holes scattered around (I'm guessing that this is illegal, too).
Everything in life is compromise. While landfilling waste might not be a perfect solution, it is no where near clear to me that it isn't amongst the best of many bad choices.