In Tokyo Ghoul:re 2 , episode 11, Ghouls from the group of Kaneki like Nishiki were worried all people from Tokyo becomes Ghoul. Why is this so? Why if you are a Ghoul are you going to be worried other people becomes like you?
From what I understand, I see two reasons:
- Goat and CCG are both working together on the last arc. Similar to what @ani's answer mentions, Goat was not an anti-human organization but rather, an organization aimed in finding ways for humans and ghouls to co-exist. It would be against their purpose if members would want for all humans to become ghouls.
- It would affect their food supply. Ghouls feed on humans. If humans would continue to become ghouls, their food supply would drop. Sure, they can cannibalize but from what is seen in the manga, ghouls do not taste as good as humans or half-ghouls.
During the last arc all investigators, as well as ghouls society, were joined together to defeat the main villain. During that time everyone were convinced by Kaneki that ghouls and humans should leave in the same place happily without harming each other. So from the above explanation, you may have noticed that the Goat organization created by kaneki has one and only single policy to protect others as well as humans. It's fairly straightforward that goat does not want more ghouls to be hunted by CCG and so to happen that, they were afraid of all humans becoming ghouls and more severe hunting would be there and CCG will not cooperate with them for sure.