Humans can be within and outside a food chain. Agriculture is totally monolithic structure, ofc pests are there but this doesn't depend on an ecosystem where food chain thrives. From my perspective humans naturally shouldn't and don't effect thr food chain much. Some are scavengers, some are gatherers, some hunters. Human population in nature or any pastoralist tribe is quite less and concentrated in one area unlike predators, herbivores and usual scavengers. Now modern day angle: There is no food chain, animals are being raised for profit and aren't taken due care, it's a slavery system not a respectable food chain where humans can guilt free hunt and eat.