In certain places of the world, particularly, our ancestors had cause to eat meat in order to survive. In harsh winters, particularly in North West Europe, it would have been almost impossible to survive without the wearing or furs and skins and the milk of a dairy animal. I have often wondered how I would react if all systems were to collapse leaving me to fend for myself in my native country - how efficient I'd be, whether I have the green skills, or whether I'd still starve in protest. I don't believe I would starve, but for now I'm not going to be ruled by a rhetorical scenario and live in the most ethical and responsible way I can whilst taking advantage of the infrastructures. If such a doomsday scenario were to befall us, it would certainly address the sustainability argument if we all went back to homesteads and created nothing beyond its use.
It is, however, very possible to be vegan today in almost all parts of the world. The only reason we keep eating meat is because we can, because it is status quo, and because we have disassociated the taste of it; because you can, you know you can, therefore you do. That is one of the awful human conditions. Whilst all other aspects of our culture appear to have evolved, and we embrace technologies and globalisation, we have left our diets behind - mostly because there any many who feel it is most convenient to do so, especially when wrapped up into an argument of 'culture'. However I do believe that very few societies have a right to this claim, and they are mostly the remaining indigenous cultures that we have - certainly not those that benefit from the fully-vamped system of contemporary Western life.
Besides that, I'd have to say that to recognise 'interconnectivity' does not mean that killing or not killing animals is primarily an emotional choice. Today it is just as pragmatic as it is ethically-driven. But to say 'emotional' is, again, very dissociative. To realise our common side-by-side existence as a community of living beings on this planet does not need to be emotional, spiritual etc. because it is simply fact as well. It can, therefore, be a matter of principle or a rationale which is not emotionally based. That is how the ancient Greeks established their own interpretation of pantheism, after all.
I have always enjoyed this little clip. It's a fun cartoon, and who doesn't love a fun cartoon - or maybe I'm just being lazy because right now I don't want to pull up all the various scientific references.