Vitamin b12 is necessary for red blood cell creation. It is made by a bacterial fermentation process. Humans do not ingest enough of the bacteria in their diets to supply enough of their own b12. To compound the problem b12 is a large molecule that is difficult to absorb. Most b12 supplements are created from animal sources, though some are created directly from the bacterial fermentation process, but the cost of producing enough b12 through these processes to supply everyone with enough b12 would be prohibitive. As such, consuming animals is necessary for the health and well being of a vast majority of humans.
Furthermore, all animal life requires the consumption of other life forms. If you want to differentiate between sentient and non-sentient life as though you fully understand what that means, you are free to do so.
The way we raise animals, in some cases, is unconscionable, but properly raising, and properly grazing larger numbers of livestock animals can both reverse the supposed causes of supposed anthropomorphic global warming and feed more people. Search planned grazing for more information.
As far as growing food in controlled environments, though sounding ideal, has not proven to be cost effective enough to replace traditional farming practices, though I personally hope future developments change this fact.
As for laboratory grown meat products, again, I'm all for it, but it's a long way away from fruition, and even further away from cost effectiveness. I have my concerns about food production being done entirely in controlled environment settings, because food supplies would be highly sensitive to any disruptions in social order, which will spiral quickly out of control once food becomes scarce. I favor more natural and humane food production that work with natural cycles over highly controlled food production. Anyone who believes that they can live without somehow exploiting the lives of sentient beings in one way or another, to one degree or another, is suffering from a severe case of denial. I support your right to limit your reliance on the exploitation of sentient beings, but I don't support your hypocrisy in telling others they should eliminate their own reliance on the same.
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