Environmental impact of meat production is one major one, but it depends on what meat we're talking about. Beef and similar are absolutely terrible from an environmental perspective. It takes significantly more water and space to produce comparable quantities of beef to other meat sources, or plants. Chicken and Turkey are usually better on that score.
It's also helpful to note that slaughterhouses have broad, measured psychological impacts on the community. They are often pushed to butcher at unsafe speeds and the killing of animals for an entire work day has a negative impact on the mental health of the workers. The installation of a new slaughterhouse has been associated with increased crime, domestic violence, and drug abuse in the community, and isn't replicated in new factories for manufacturing, lumber processing, paper mills or other similarly sized factories.
Killing for a Living: Psychological and Physiological Effects of Alienation of Food Production on Slaughterhouse Workers - https://core.ac.uk/outputs/54847380
Additionally, Upton Sinclair who wrote The Jungle, which is largely attributed with launching public pressure to create federal reforms for more sanitary meat packing, originally created this to highlight how it fucked up the workers: https://en.wikipedia.org/wiki/The_Jungle
That's true on the current margin in the US but only on the current margin. Creating one more pound of beef than we currently do does require a lot of farmed soy and other crops and ends up very inefficient. But there's also a lot of grazing land in the US that can't be used for intensive agriculture and provides a lot environmentally "free" (minus methane emissions) meat. From an environmental standpoint we want to halve or so the amount of beef we consume, not eliminate it entirely.
And other countries than the US are operating on differnet margins.
Maybe so, but if we only focus on "efficiency" we're going to end up living in dystopian nightmare, a very efficient one. Specifically regarding food, eating is not something purely functional for humans who are not seeking maximal efficiency but also enjoyment.
In Western countries population is already naturally dropping. What's needed first and foremost is a culture shift so that we stop seeing that as a negative. In any case, we have no choice because population cannot keep growing indefinitely in a finite space (which is what would lead to an actual dystopian outcome and we are getting there just looking at the state of the environment).
The very fact that you replied what you replied just now after I mentioned population levels shows how the public has been conditioned.
Compare: "In Western countries vegetarianism is already naturally rising" ... "What's needed first and foremost is a culture shift so that we stop seeing meat as a necessity" ... "We have no choice because livestock supply can't keep growing in a finite space" ... "The very fact that you commented as soon as you saw an anti-meat sentiment shows how the public has been conditioned" etc.
