What people generally oppose today is a function of their consciousness and ability to access alternatives. They don’t oppose slaughter because they don’t think there’s an alternative, the same way that a person who is on the verge of starvation will steal food. They also don’t oppose slaughter because it’s hidden away from them, and done by others.
Slavery is an excellent cognate to this.
It’s a slippery slope, isn’t it? If you’re not careful with your compassion, you’ll end up having it for all sorts of beings you’ve come to see as like yourself.
> They don’t oppose slaughter because they don’t think there’s an alternative
That's clearly not true, and a projection.
They don't oppose slaughter because they find no objection with killing an animal for nourishment, "necessity" having no bearing.
> Slavery is an excellent cognate to this.
No it's not. I always find the idea that humans are not in some way special (at least to other humans) off-putting. Even animals treat members of their own species generally better than they treat other species.
I love animals, I think we should treat them with dignity and respect as much as possible. At the same time I would not hesitate to kill an animal for food or if it endangered another human.