Steveo,
I believe NH has a "Zero Tolerance" for gray water discharge on land or in the water so technically that person is probably breaking a law there. Even though there are much greater 'discharge' violations taking place at every beach it is still kind of rude. I know if I saw somebody doing that I would say "Eew yuck!"
If you're really squeamish, dont drink city water in Laconia!
As for the mooring itself, I am pretty sure only the land owner can file the application but can authorise anyone else to use it. A tenant usually has the same rights as a landowner but the clerk might ask to see the lease. I wouldnt want to bet a large sum on how that might turn out, either way. Especially for a seasonal or short-term rental.
As for the "slamming" that sometimes goes on, It can get a bit "rough and tumble" on the internet. Due the anonymity sometimes people feel less accountable for their words. I have a fairly thick skin myself and try to interpret how folks post with the benefit of the doubt. Most folks here will apologise or back-peddle a bit if you suggest they seem a bit over the edge.
Hang in there!