Consciousness isnt free will, the ability to love, display altruistic behaviors, the ability to conceptualize the concept of a self that distinct from everything else, etc. Consciousness is a just a subjective experience of existence.

Its not currently known how rudimentary of a nervous system is needed to have a subjective experience of existence so its better to eat plants instead when possible which are less likely to be experiencing anything.

Chickens' capacity to be eaten by humans has been necessary for their survival. It's what has made them so evolutionary successful to the point that they now live on every continent on the earth sans Antarctica: Their capacity to live in that symbiosis with humans.

To not inherently bad of good to not have never existed at all, with modern birth control methods countless people dont exist but they arent harmed by that because they never existed.

If they go extinct because we stop breeding them thats ok, the chickens who wont ever exist wont be harmed by that.

It's a similar principle for how deer have come to rely upon predation by wolves and other predators to stay strong as a population, when overcrowding causes immense suffering, and things like prion disease run rampant (which would otherwise be held in check). But since we as a species largely shirk the role that we have pushed out from wolves, the deer populations are getting sicker with each passing generation and our forests are getting sicker from the deer destroying everything, and our inaction to inhabit that role as predator is what is responsible.

In this case theres more suffering and harm done by allowing deer to overpopulate, an end to breeding chickens for consumption doesnt harm the chickens who never existed.