What is your evidence for that? It seems that equality and universal human rights are so new, there's hardly time to judge them to see how they stand up to the Roman Empire and some of the really long-lasting societies. I'd say they've barely been around a hundred years, as a widely accepted ideal.
It may be true, but I'm suspicious because it seems too close to arguments that whatever "we" are is the pinacle that all previous time has been working toward, like the last upright guy on the evolutionary chart. In fact, we're just yet another midway point. Inequality and slavery have at least appeared to be instinctive for many more years. Our thoughts could just be a temporary glitch, or could be okay but maybe we're missing something even more important that will show up in a century or two.
The thing is, there were always people who said slavery was wrong on moral grounds, and argued for it.
The appearance: sometimes slavery has been socially acceptable. Well, that could be because there's no such thing as morality, or it could just be because people accepted something they knew was immoral, because it was convenient or lucrative. Again, often in society, people pay lip-service to something in order to fit in, but don't express what they secretly think, until someone else has the courage to stand up and say it, and a tipping point is reached when everyone feels it's ok to say it. (This may be the case with religion, generally: obviously, as it's become less of a risk to life and limb to declare one's atheism, more people come out of the closet, but as Dennett's survey of priests showed, if you're still committed to something for various reasons, you may still choose to follow it, even if you don't agree with it.)
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Great thread, with some good, deep discussion. My take on it is that morality is based on reason (what is moral is what any rational, reasonable person would think is moral). The "it's just a group practice" idea doesn't work as a standalone, because it just devolves to that (analogously to the argument re. god willing it because it's just - a group picks a morality because it thinks it's reasonable to do so, it's not the moral thing because the group picks it).
Moreover, it is a form of instrumental reasoning - IOW, all moral reasoning is "if ... then", therefore it's all in the context of a goal, aim, perspective, ideal or purpose.
So far, then, it would seem to be amenable to scientific rigor and analysis.
There are two problems left: the universalism of morality, and the fact that it's understood to override personal preferences sometimes. These seem to imply that instrumental reasoning as the basis for morality is not enough. (i.e. it's not enough to explain it as a matter of "if ... then you ought to ....", with the "if" usually tacit).
Re. universalism: it's understandable that groups follow moralities because they think it's reasonable to do so, in light of certain ideals, goals, etc. But the sticking point is, where does the universalism (that we feel instinctively is part of morality) come in? Why should it apply to all, and not rather only some?
Re. personal preference: normally, the moral thing to do may override one's personal preference. Were morality purely instrumental, then there would be no reason not to steal a purse that's been left on a bus when there's absolutely no chance of you being caught out, for example, whereas we all know the right thing to do is hand it in, even if it's a potential personal loss.
The solution to this can only be found in mystical experience, IMHO, in terms of both the intimations people have in everyday life, and in the traces of it, in more powerful personal forms, in religion, which then become cultural artefacts passed on, and reinforcing both the personal intimations we have, and morality in general.
As a rationalist, I understand mystical experience to be a gestalt switch in the mind, that makes it flip over from seeing the world in terms of separate things (which is a true way of seeing the world), to seeing it in terms of being a single system (
also a true way of seeing the world, not exclusive of the former), with one's sense of self-identification switching over to the system as a whole, instead of the part. I view this as a fully functional cognitive understanding, as it reveals something self-evident that we all understand intellectually, but don't normally feel, or see the world in perspective of.
And I think it's from this cognitive understanding (of the "unity" side of nature, through unitive experience), its instances in most peoples' experience, and its traces in culture via religion, that the universalism of morality comes. Were it not for the fact that some people had these kinds of experiences, and some more powerfully and completely than others (thereby founding religions, which then usually devolve to social control systems as the original message gets garbled through "Chinese Whispers"), there would be no universal aspect to morality, there would be no sense that moral reasoning should override personal concerns (other than when it's convenient to do so, to
appear to be trustworthy). Morality would then have a group/relativist explanation only.
When the unity side of things is understood and felt, and the more it is understood and felt, the whole is what one automatically "cares for", without essential distinction of self or other. This means, practically speaking, that morality is of universal purport (via the Categorical Imperative), and also may override personal concern.
This latter has to be looked at carefully though. Morality is not (or rather I believe ought not to be) considered as essentially altruistic, it's just that the concern is for the whole,
oneself not excepted; but this means that sometimes others' needs will weigh more than one's own. (IOW, morality is essentially neither altruistic nor egoistic, but holistic. This means that concern for personal virtue and personal flourishing is as much an aspect of morality as helping old ladies across the road.)
When morality is thus understood to be instrumental and largely consequentialist
in that broader context of mysticism, with its universal aspect having a rational explanation in a cognitive experience of unity and lack of essential or intrinsic distinction between self and other (those being only conventional and convenient distinctions, relative truths), then the way is clear to a scientific understanding of morality, there's nothing philosophically suspicious about it any more, and nothing particularly philosophically problematic any more. It can be instrumental through and through, while retaining the universalism that seemed to contradict the instrumentalism.
With this position, though, I'm in a three-cornered fight: the rationalist is going to baulk at my invocation of mysticism (even though I naturalize it), the religionist is going to dislike the derivation of morality from reason alone (as is traditional with religionists).