I'm not assuming healthiness is binary or even defining healthiness. The only statement I'd say is that humans can efficiently and successfully extract energy and nutrition from various critters we ingest. We extract a good amount of it into useful things, and have much less waste than, say, plants, as we have no real ability to deal with cellulose like a ruminant would. In out evolutionary lineage, primates (as well as many other creatures) are omnivorous, and I'll assume we have whether vestigial or otherwise, the same omnivorous abilities. Whatever caused that phenotype to express itself, whether polygeny, pleiotropy is related or if it is merely an expression because of some other characteristic like the immune system (to make one up), doesn't really change the fact that humans are able to utilize other animals as food. It would follow since there are plenty of animals that use other animals for food, and I would think that its to our benefit that we can, since we lack most offensive and defensive capabilities that other animals do. No fangs or claws are built in. We do have tool use to compensate for that luckily. Since most organisms consume other organisms (plant or animal) for their needs, then our ability to be so widely omnivorous, compared to the relatively specialized diets of other creatures, allows us to have an advantage since we lack those limitations.

Meat isn't the healthiest thing for us, but I'd say that meat and animal fat, more related to things our bodies need, is far superior to processed sugar which is far more unhealthy and damaging, something I also avoid ingesting (sugar that is). Our bodies are horribly designed for refined sugar, and our type 2 diabetes rates are certainly helping show this is the case.

Points 1 and 2 you made are related. It's good for us in absence of nothing at all. How it rates in comparison to other food options for out omnivorous consumption is certainly a valid question. Your third point is what expresses the phenotype, which is certainly based on our evolutionary ancestors, so its not surprising that we have the ability.

I don't eat meat personally, and I'm not arguing for meat consumption, and in a variety of ways people should consider avoiding it (although I'd still say avoiding refined sugar is, health-wise at least, more important). There are "better" things to eat which are closer to the things we actually need to eat, nutritionally, making the animal middle-man not necessary, but that's a separate discussion.