it just doesn't really make sense tho, why dont you want people to be able to fish, what are they stealing from you by fishing? if anything it brings people to your residence if you have a shop which most shop owners want.
Shore fishermen are littering scoundrels. Not a day passes by that I don't find worm containers and soda cans down there by the river. Git off my lawn, I say. More seriously, I think people have a desire to have control over something they have put effort into. It is the same reason Wild Protections are so important to so many of us. It is similar to how people dislike shop re-sellers. Sometimes it can give you the feeling that someone is taking advantage of you. Personally I like to have people come fish at my pond and to know they enjoy it. But I don't have to agree with it to understand it.
It is our goal to ensure the server is simple as well as flexible. Things that can not bring harm to the owner of a residence is things we would rather keep simple and not add flags for. Which is why I even recently removed use flag requirements from enchanting tables and workbenches (and enderchests never required it). Players using those items on your res does not cause you harm. I would say if keeping people from fishing in your pond is a big deal, to simply build a building around it with a door and only give those you wish to fish there access to the doors with access signs.