in all fairness though they're very cute and there's nothing wrong with making the entire outside portion of your fortress a giant equine/goat/cat/bird sanctuary for your animal trainers to frolic in while you send miner after miner to their watery graves (after all three of the fortress' military squads were killed or maimed fighting two forgotten beasts that made their way out of the caverns into the hallway leading up to the fortress) in the cavern fifteen layers beneath all the unicorn vomit....we're rich in rope reed and barley
I've had several fully vegan fortresses. The issue is that idiot dwarves get one of their stupid moods and decide they'll die if I don't provide them with animal bones or leather or something. I've lost dwarves this way, so now I buy animal products from caravans to avoid it. It's a shame, really, I wish I could convince my dwarves they don't need to make bone necklaces, we have so many gems and silver and all kinds of things that make better crafts than animal bones!