If you don’t eat chicken nobody is going to swoop in and eat all the chicken you don’t eat. However if a farmer or farming corporation decides to stop harvesting chickens then it’s almost certain some entity will swoop in to replace them in the market. So acting like the consumer here is not one of the if not the most important part in this causal chain is just naive.
That’s not important. I was illustrating that clearly if nobody ate chicken nobody would harvest chickens for food. Unless you think that the same amount of chickens will be harvested until the very last human gives up chicken then you have to acknowledge that the individual consumer does make a difference.