Is there no urge within? B12 is a vitamin that's naturally found by eating animals. I'd argue it's a more natural source of B12 than taking dietary supplements.
I can understand the ethical concerns behind not wanting to eat meat - but likening it to slavery is silly. There aren't any vitamins I can only get from eating a slave or taking a pill.
Also wouldn't owning a pet be more of a slavery situation than domesticated animals used for food. But cats and dogs in their current state are also a product of evolution. And I think our hunter gatherer ancestors settling down, starting farms and domesticating animals, is another product of evolution. Instead of traveling like a hunting pack, they could settle and form a civilisation.