And isn't unnecessary killing always unethical?

Humans are omnivores, not herbivores. The implication here is that some animal killing will always happen. Unless we hit some technological singularity beyond which we can subsist on clean meat.

Also, every plant food you have ever eaten contributed to the death of some animal.

Agriculture is not natural.

It displaces entire species and causes the death of countless animals via direct mutilation (combine harvesters) or via pesticides or other means.

Your physiology is geared toward at least some animal foods, and agriculture results in killing anyway. Therefore, logic would suggest that you might as well eat meat.

You can avoid factory farming if you want. Farm share, for instance.

Vegans are not morally superior to others. They're just in denial.