yes yes, if mutual.
Humans feed on poultry, but microbes, bacteria, lices, worms, feed
on us. (even when we are alive).
So nothing much really. The bad thing they fail to see is that
culling will not solve things long-term.
To be ethical rather, though not financially sound, we should show
empathy to the chickens etc, by trying to find a cure for them and
help them, right?
Definitely, not kill them. 
So, let's say your mum got SARs or some uncurable and infectious
disease, you kill her? (touch-wood)
