First question I would ask in response to his questions is whether he would be asking these questions of cat/dog/fish/cage-bird owners. And I would not give specific answers for what any single individual's plans are.
You might answer that there are many purposes that people have for raising chickens, to include exhibition, 4H, pets, eggs, meat, insect control, yard candy, source for tie flying feathers, etc.
Chickens are available from many sources including breeders, hatcheries, feed stores, other backyard chicken enthusiasts, school hatching projects, etc.
How I would handle a neighbor's complaint would depend on the neighbor and the complaint. A legitimate complaint (birds hopping the fence into their yard, excessive noise, odor, flies, light from coop keeping them awake, etc.) would be handled as soon as the issue is known, or prevented fro the get-go. Something like "I don't like chickens" or "chickens do not belong in this neighborhood" are not really legitimate complaints. Some people do not like cats or do not like dogs, but as long as those animals do not create an actual nuisance, those are opinions, not legitimate complaints, and I would ignore or respond to them the same way as if someone said "I don't like your car" or "I don't your dog."
Most cities enforce code violations only when there is a complaint, and then only to the extent that there IS a code violation.
Some cities require permission from adjoining neighbors, but that is not really a good solution, and many cities do not require neighbor permission. Adjoining neighbors can change their minds, or sell their house and a new neighbor moves in. The cost to acquire chickens can vary from a couple of dollars for a chick at the feed store to several hundred dollars for a show bird. Cost and time expended for purchasing or building a coop and run or installing an escape-proof fence can also be considerable. It is not fair to let a neighbor decide what one can/cannot do on their property so long as no actual nuisance is experienced. Anyone MIGHT open their windows and play their stereo at 150 decibels, rendering the neighbors deaf, but to regulate the owning of stereos because of what MIGHT happen would be deemed silly by most. Ownership of chickens should be viewed the same way. Define and regulate actual nuisances, not their cause.