are vegetarians more ethical by not eating meat?

[littleendian]

However a significant number of humans, around 400-500 million in total or around 7 percent of the global population, exist on a plant-based diet, which shows that we do have a choice between eating meat or not eating meat and hence it is not primarily a biological question but rather a moral one.

By default? I think you may have left out quite a few other possibilities.

You may refer to the argument that meat-eating is actually necessary for some people, depending on their individual biology (?)

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To clarify, you feel that there is a justification for killing an animal for food, if it's absolutely necessary to sustain a human life?

Yes, I don't think its possible to attribute any kind of moral value to any act that directly serves self-preservation in the face of death.

Does this cover other areas? Such as using animals for scientific research and testing?

Of course, although this is much more ambiguous than the question of diet at least in the medical science because it's impossible to quantify the suffering of the lab animals against the human suffering that it might prevent. Cosmetics is quite a different matter though.