You seem to be implying that morality is subjective, which I think is a dangerous belief. People may believe their actions are ethical, but that doesn’t necessarily make them correct.
Jonathan Haidt's work on "Moral Foundations" could be worth investigating. They determined 5 major cross-cultural "moral foundations," to which each person assigns various degrees of importance: Care, Fairness, Loyalty, Authority, and Purity, suggesting these stem from a biological/neurological source. From Wikipedia:
> Haidt and Craig Joseph surveyed works on the roots of morality... From their review, they suggested that all individuals possess four "intuitive ethics", stemming from the process of human evolution as responses to adaptive challenges. They labelled these four ethics as suffering, hierarchy, reciprocity, and purity. According to Haidt and Joseph, each of the ethics formed a module, whose development was shaped by culture. They wrote that each module could "provide little more than flashes of affect when certain patterns are encountered in the social world", while a cultural learning process shaped each individual's response to these flashes. Morality diverges because different cultures utilize the four "building blocks" provided by the modules differently.
Perhaps these four "building blocks" -- suffering, hierarchy, reciprocity, and purity -- are sufficient for an objective basis upon which an intersubjective understanding of morality can be determined.
Then again, even the notion of objectivity is questionable and culturally-dependent...
Okay, but it's important to note that studying the evolutionary and neurological bases for morality give us a description of morality, not a prescription for morality. In other words, Haidt can only describe how people behave, he can't prescribe how people should behave.
There's a big logical leap between (for example) observing that many cultures proscribe lying, and saying that one shouldn't lie.
1. Some philosophers have a descriptive ethic (this is what people do) rather than a prescriptive ethic (this is what people should do). This is certainly interesting, but it isn't what most people mean when they talk about ethics--it doesn't give us any guidance on how to behave ethically.
2. Some philosophers try to work backward to a prescriptive ethical principle from a set of ethical prescriptions which are widely accepted but, importantly, unproven. For example one might start from the prescriptions "murder and lying are wrong, giving and learning are right" and attempt to come up with a prescriptive ethic that unites these prescriptions. But "murder and lying are wrong, giving and learning are right" aren't objective facts even though they're widely accepted, so any prescriptive ethic that comes from these prescriptions can't be objective either. It's not coincidence, for example, that in the west, the atheist/moral realist philosophers mysteriously often start from Judeo-Christian prescriptions.
My impression of Harris' morality from videos I've seen of him is that, like most ethicists, he's attempting to work backwards from existent ethical prescriptions to find fundamental prescriptive ethical principles. The fact that he's sourcing the ethical prescriptions from scientific method rather than religion means that the prescriptive ethical principles he arrives at are more palatable to people like me who practice science and not religion. But he's still starting from the unproven assumption that the ethical prescriptions he's started from have objective validity. As such, I don't think he's arrived at an objective prescriptive ethic any more than anyone else. I think you should practice the scientific method if you want to understand and operate in reality, but I don't think that practicing the scientific method is an ethical imperative.
That said, I haven't read the book you mentioned, so there might be something in that book which isn't in his talks which would persuade me.
I don't believe that myself, but I do believe that people advocating for a specific ethic are usually supporting their own point of view, which may be closer or further away from the ideal.