How do religious people justify raising and slaughtering animals for food?

[Angrboda]

There's even a globally common hierarchy of sacrificial value.  Plants, barring specifically denoted sacred ones..ofc, had relatively less life than animals.  Easy to make the connection.  They just sit around most of the time, doing a whole lot of nothing.  Animals, again barring specifically denoted sacred ones, less than human beings.

Over and above all of this, there was greater sacrificial value to any of the above when it was dear to us, commensurate with the level of affection and pain that would be experienced by it's loss - the very nature of sacrifice....

-ergo.

Then God said, “Take your son, your only son, whom you love—Isaac—and go to the region of Moriah. Sacrifice him there as a burnt offering on a mountain I will show you.”

Like the dragons in the garden, when god was small and the earth was young and the first people walked....he was content with sheep and goats from herdsmen.  By the time of Isaac he is fully grown, and so too is his appetite.

Feed him here at the alter, and you will feed him there on his throne.  Perhaps he may not feel so hungry later in the night, while you're sleeping.

I always get a kick out of how the penance for having your period was that you sacrifice two pigeons to God. Maybe that was God's way of managing the burgeoning pigeon population......