Why I am not a vegan

[Monica]

Does "doing so" in the final sentence refer to eating meat or causing unecessary suffering (or both)?

Being that the human body doesn't require meat - and this is proven by science and agreed upon by the mainstream medical community - then all eating of meat is biologically unnecessary. (There may be some logistical issues which may make it temporarily necessary, such as indigenous tribes whose livelihoods are intricately woven with the killing of animals, but biologically it's unnecessary.)

Being that all slaughter of animals for food is unnecessary and a violation of sentient beings' free will to live, then it follows that:

Knowing that it's unnecessary, and knowingly choosing to do so anyway, is inherently STS.