I need to think more about this, and I guess I'd need an argument that specifically addresses the weaknesses of ontology. But I think the issue of whether eating meat is ethical or not hinges on 1) deciding animals are worth considering as morally relevant and if we do 2) what actually will bring about the best result for all moral agents- human and animal alike. I don't think 1)can be answered through anything but a decision to do it- to decide that the suffering of animals matters. No argument will decide it.
To answer 2) will need a lot of knowledge of how the actions of billions over time impact many enormously complex systems. I don't think there's going to be one blanket proscription that is going to work for everyone everywhere. But I'm not totally sure about that.
All of this suggest to me that ethics for the real world is going to have to be much more bottom-up. It really always has been- professional philosophers just were mostly not paying attention.
Scattered thoughts again, but I don't want to stop myself from putting stuff out there. I can always go back and correct myself.