....Do you think sailors litter more or less than non-sailors...
I'd be willing to bet sailors litter less than average.
However, the average litter is a coffee cup, beer can, wrapper, cigarette butt, or other sundry junk that was intentionally or unintentionally discarded. Cruisers are trying to dispose of a weeks worth of household garbage. Publicly available containers are most often established to capture the sundry trash or trash remaining from a single meal, not bags worth. I've routinely seen containers, typically near dinghy docks, overly piled with kitchen garbage bags, which I think is just as poor as tossing a single can on the ground. When the container was not designed for household garbage, one is just taking advantage, by forcing another to clean it up. Same as using any receptacle that one does not have permission to use. You can't rationalize an entitlement.
The best programs are those that either ask for a fee to dispose of a bag of garbage or charge a small landing fee for everyone that comes to shore. These are then used to provide services to the marine community, such as the docks themselves, trash containers, water, whatever. I gladly pay a few dollars to dispose of a bag of garbage.
Like I've said, I've asked permission to use trash containers and almost never been turned down. There is a marina we go to on an island that specifies they do not take trash. They make this clear. It's extremely expensive and this island requires extreme segregation (glass, plastic, food, paper, non-food, hazardous). They don't take it, because there is not container for general garbage and no boat does this much separation. I asked if could just pick out my large containers, separate them and use their containers once. They agreed to once, just for those bulky items. If they saw a transient using the containers without permission, presumably rationalizing that they paid for their slip and despite the prohibition, they'd be evicted and banned. Rightfully so.