This post contains minor spoilers, but if you’re having trouble with the contrivance of the book, I think this will help.
Tender is the Flesh is not first and foremost genre literature about a future where we eat people and exploring that space; it is an allegory for how under Capitalism we treat people as commodities.
Now to the spoilerey bits:
You find out over the course of the book that the virus is just made up. The ruling powers did so in order to justify the mass imprisonment and slaughter of immigrants and the poor.
If you think “there’s no way people could become comfortable with this level of oppression in a single generation”, the book leads us to realize that we already live in a world where much of the horror of the book is currently happening and yet the vast majority of people go on with the lives anyways.
The bit towards the end where they describe a dog walking around with it’s entails hanging out made me so nauseous I threw up.