There's a large group of loud children on a service I take semi-regularly. I want to relax when I'm going home and you best believe I am hogging that table seat because they always seem to take up two bays next to eachother. They usually end up walking down the train and shout at eachother far enough away that it's not problematic.I don't usually go for table seats if on my own, as they are more likely to fill up, and it feels a bit "selfish" to be sitting at one if a family of 4 comes along.
It's not a particularly busy service, so I don't feel guilty. There's a free table for slightly smaller groups (3-4) opposite the aisle.