There is nothing in the ToS that states that two people cannot fight in the same channel. It is against the rules to steal other people's kills, but if you are fighting in a completely different are of the map, that is completely your business.
Stop whining about people stealing your channel when they're simply trying to train.
Populated areas, such as Jesters and Scarecrows, will always be full, so stop acting like you're entitled to have one huge map all to yourself. It's petty, selfish, and frankly, reminiscent of a four-year-old screaming "mine!" when someone wants to see his toy.
If someone is killing everything around you so you can't get anything done, that's KSing. If someone is at another part of the map and killing monsters, they are sharing the channel with you. There is nothing against the rules of the game in that, and if you're seriously upset that you're not getting every little monster to yourself, that's your problem.
That is all I have to say. Grow up or quit.