This is a really interesting position, I'm interested in how you arrived at it. Do you think that if killing something is fun it will result in more things being killed, or is your issue more fundamentally with the idea of killing being fun?
It is a hard ethical dilemma and any line you draw will be arbitrary. Some people hunt rhinos, some catch fish or shoot birds as past-time, while others get sense of satisfaction from gunning down insects. I still condone pest control, but I draw the line at reasons like "for fun", or "because I'm bored", or "to feel more powerful". The intention/reason is important, because it affects the future. If you do it for fun, you have no reason to ever stop or to consider alternatives once they are made possible.
To answer another post, I think killing in video games is completely OK and something I often enjoy doing.
I'm also enjoying the tone you've set for discussion and I'd like to hear your personal views.
Essentially, my stance is that there is a difference between accepting an action as necessary and engaging with it as needed and making said action fun / associating it with enjoyment. I don't count video games as part of the issue for the moment since, at least currently, it does not seem like the characters and units that populate video games are in any sense alive. This may change, however, and if it does then I expect radical consequences will unfold.