This:

"But such killings happen every day, do they not? And I would daresay that what one person considers “warrantable cause”—He was raping my child; She was having sex with a man not her husband; He didn’t show me enough respect; The baby just wouldn’t stop crying!; She brought shame upon our family—another will not."

seems to implicitly assert that an objective reference to reason is impossible with regards the ethical nature of a given act. I don't see as you're actually saying such but it could be inferred from that. This begins to explain why rights-theory advocates (such as myself) get something like an immune reaction when someone says, "natural law/natural rights is all nonsense anyhow" and the response is usually pure vitriol. It's impossible to bridge that gap, however. What is euphemistically called "non-cognitivism" is in practice a denial of the possibility of the use of reason in constructing a theory of ethics, but its implications are far more broad than that, and far more disastrous, and sure it is no wonder that it is a product of logical positivism.