I don't really get these arguments. Would it be better if there were just a few chickens kept in zoos. That seems to be the alternative.
It is an interesting question, isn't it? I'm not saying I believe that, but really, which one IS morally better? Is the numerical population of your species a moral good? Is it the average quality of life? What if the chickens had a great life and got surprise-killed, never knowing harm? Does that make it ok to kill them? Or is killing them not a moral problem to begin with?
The article alleges that eggs are not free from killing because only females lay eggs and therefore half the chickens hatched to produce egg-laying chickens are killed because they are male.