Copyleft licensing in this analogy becomes a legally enforced way of ensuring that a vegan recipe can only be used in the preparation of further vegan or vegetarian recipes.
Many folks are fine with that, but some complain:
- this isn't fair to meat eaters that actively refuse to eat vegan dishes (rather than merely preferring to eat meat)
- this isn't fair to people that actively refuse to create their own vegan or vegetarian dishes, and hence can't make use of the vegan recipes, even when they're really tasty