How about something like "Should we allow chickens to be raised in urban areas or should they be confined to the farm?"
This is a very good topic for a persuasive argument that continues to make the news in many cities. Your teacher may still not agree that this is a good topic due to his own lack of knowledge on the topic, but you could show him a few newspaper articles from across the country where this is a current, highly debated topic.
It allows you to talk about the benefits of chickens as you mentioned and lets you branch into the growing popularity of "backyard chickens". There is the pet factor, the economics of raising your own for eggs or meat, the consolation of knowing that your food is raised humanely and without adulterants, self sufficiency, "green" living, etc. Then you can spend all kinds of time debunking the popular chicken myths that abound.