That's weird.. My grandparents are from England and have eaten plenty of roosters in their days. They are the ones who explained to me how to kill them for meat.
C02 doesn't taint the meat, and it is how they kill rats and mice for reptiles, so I can't see it being much different with chicks. However, I personally would use them for meat. Free range them and have some nice slow cooked roosters in 16 weeks.