Does ethical philosophy build normative models that describe what ought to be? Sure. Do these models influence actual human behavior? Not a bit. So why bother building castles in the sky?
Ethical views regarding natural rights are the basis for liberal democracy, either (depending on your metric) the largest or second largest form of political organization today. I'd call that "influencing actual human behavior."
Ethical views regarding harm reduction form the basis of modern medical treatment. "Do no harm" is a normative statement, and I know plenty of doctors who seem to be influenced by it.
These are the simplest of examples. Abrahamic religions encourage their adherents to behave based upon duty, another normative staple. Individuals act based on rational self interest, and a great number of philosophers have argued that they ought to do so. The list goes on.
Philosophical systems of ethics have always seemed to me like elaborate rationalizations for what we all know to be right and wrong innately. Since most of us possess this faculty with or without philosophy, the formalization is just self-flattery.
Do you think healers sought to do harm before Hippocrates came around and that the mere phrase "do no harm" ushered in a new era of helpful medicine?
The evidence for this claim is scant: the Ancient Greeks (and not-so-ancient Western Europeans) extolled the virtues of various forms of slavery, all of which we find morally reprehensible today. Moral views of abortion, homosexuality, and blasphemy have all undergone complete reversals in the last 150 years. Intuitionism alone can't account for these changes.
> Do you think healers sought to do harm before Hippocrates came around and that the mere phrase "do no harm" ushered in a new era of helpful medicine?
Hippocrates formalized and systematized what was otherwise a naggling feeling. Just because doctors happened to perform in a morally acceptable fashion pre-oath does not mean that the system prescribed by the oath is redundant -- it serves to establish why certain procedures are right and wrong, when a doctor might be punished or blamed, and so forth.
This is all correct, which is why I said "intuitionism alone". The reason is the absence of a clear causal connection: our (meaning the general public's) moral intuitions have developed in tandem with political and economic progress, not as a cause or purely as a consequence of it. Combined with the massive volume of political and ethical theory produced shortly before the emergence of the world's first liberal democracies, I'm inclined to believe that the causal arrow goes in the other direction than the one you suggest.
Using the word murder is cheating. Of course an "unlawful killing" is taboo, it's in the definition! Killing humans is definitely not a universal taboo, just look at wars and those that support them. Since all ethical statements have an evaluative piece to them, we cannot say anything is universally taboo.