When factory-grown meat takes over the shelves of meat departments, cow and chicken population of the world will dwindle significantly. Only milk cows and egg-laying hens will remain, along with a small population grown specifically for slaughter, for those perverts that prefer natural, pasture-grown certified organic meat.
Finally humans' beloved pets, cats and dogs, will stop being animal racists and stop feeding on the suffering of other, less fortunate animals.
The only remaining area of unethical killing will be the pesky wild nature, where merciless foxes eat rabbits, and brutal trouts eat lesser fish, which eats small defenseless crustaceans, which.., etc. But I'm sure that progressive humankind will find a way to sort this out eventually, too.
Irony aside, have you heard about the "first noble truth" of Buddhism? Very short and rather enlightening; google it.