to kill or not to kill gremlins

I have dropped gremlins and I believe when my friends killed them I lost goo and they gained. So with that being said if they drop gremlins in my town I kill them, gain goo, they lose goo and visa versa then their is no real benefit to gremlins as it should even out your loss and gain to being flat. Unless someone has tested this between their multiple worlds and knows for sure???