Thank you for your reply. I will attempt to address directly as many of your points as I can. Please forgive me in advance if I overlook anything or misunderstand some of your criticisms of my argument. I will also try to address your points in their original order and beg your forgiveness as well for the inevitable length of my reply. I'll do my best not to be too redundant.
You open by stating that "objective moral values is not a scientific question; it's a philosophical question." My initial response is that I'm not arguing for the existence of "objective moral values", at least not if by "objective" we mean values that exist outside of human (or anything else's) subjective experience. I am attempting to argue that morality is grounded in these subjective experiences/relationships as opposed to existing purely independently/objectively. Regardless, I don't see science and philosophy as mutually exclusive. Indeed, I see them as joined at the hip.
That is not to say that our subjective experiences and their physical/mental impacts upon us cannot be confirmed and evaluated scientifically but to argue that those scientific findings will inevitably have philosophical/moral implications. But this is not the same as arguing that the "truth" of the values themselves can be determined by strictly scientific means. If we define a moral action as anything which, generally speaking, reduces suffering then we can scientifically verify the degree to which various actions either increase or decrease suffering and thereby evaluate their relative morality, but ultimately we must accept there is no means of scientifically verifying our definition of morality is "true" in any objective sense. It is merely true that we (and virtually all living things in their own way) tend to prefer to avoid needless suffering and therefore this seems the best place to plant our moral flag. For more of my views on the often false binary subjective vs. objective categories we tend to split the world into see my essay on the subject at https://craig-axford.medium.com/objectivity-vs-subjectivity-an-incongruity-that-isnt-really-5c29ffe93c81.
In point one of your reply you tackle my reliance on evolution and natural laws. You conclude by stating: "A process [evolution] that is determined wholly by natural laws and which we cannot step outside to assess objectively. On this view we believe what we believe, not because of the evidence, but because of the chemical state of our brains and the relevant social/environmental factors."
To this I would begin by saying that in talking about morality we are talking about a process or way of being with one another. Therefore, it never was or ever could be a process we could step outside of to begin with, with or without a reliance on evolution or any other natural process. Even assuming morality was handed down to us or imposed upon us by a force that somehow was outside the system as a whole, we would very much be inside it and therefore incapable of evaluating it in anything approaching a completely impartial or objective way. What we consider to be right or wrong cannot be separated from how we feel about the fairness, justness, or suffering it causes us and those we care most deeply for. It feels like something to be treated both morally and immorally, however we define those terms, and what it feels like hardly plays a trivial role in what we determine to be moral and immoral in the first place.
But what about the evidence? Does it follow then that our beliefs are 'determined' by chemicals, genes, and other biological forces as opposed to evidence. First of all, I would say that belief is the wrong word to pair with evidence. If I believe something to be true, that there's life on Mars for example, then I necessarily lack evidence for it. However, if I say there's probably life on Mars because we've found water there and methane levels in certain places that seems to indicate there may be some simple forms of life then I am citing evidence to support a probabilistic argument in favour of life on Mars. The more evidence I am able to cite, the more likely life on Mars becomes and the less belief has to do with it.
But more to your point, yes, as a species that has evolved a highly complex brain that enables us to enjoy things like self-awareness it is not incorrect to say that evolution has enabled us to both believe and respond to things like evidence. The things we believe and the evidence we are exposed to/open to influence our behaviour which in turn influences our brains and bodies. We live in a web of feedback loops, not linear lives in which evolution determines our beliefs without any influence from our beliefs/evidence upon our evolution (both cultural and biological).
Your second point is that evolution is not aimed at truth. No argument from me. As I stated in the article our capacity to be moral actors does not equate to us actually being moral actors. That is true no matter which definition of morality we choose to adopt. I explicitly use the example of snakes, which we are primed to quickly develop a fear of in spite of the fact that very few of them are any danger to us. Evolution is a blunt instrument. We evolved the capacity to think abstractly and cooperate as social creatures. Concepts like morality were emergent byproducts of as opposed to anything like the targets of evolutionary processes. Moral progress, a concept you allude to later in your reply, is a process of trial and error, both individually and collectively and has a very uneven history. If we ultimately decide things like war or slavery are wrong it isn't because we we biologically evolved to think this but because we biologically evolved a capacity to first engage in war and slavery and then later and only slowly begin to see that over time the downsides outweighed the downsides, and not just for the losers and the slaves. It took so long for us to develop we have the views we have about things like slavery today because, for a variety of reasons, slaveries wrongness was anything but intuitive initially.
We evolved a capacity to observe and communicate with one another about the various hazards and benefits associated with these types of activities and to consider how they made us feel personally. In time, it occurred to us that the only way to keep our families and friends safe from the threat of being sold into slavery or killed in war was to avoid these activities altogether, something we are still struggling with. This is admittedly a very rudimentary accounting of moral/cultural evolution but one consistent with our long history. I could go on and on about the feedback loops that develop between technology and moral debate (i.e., written language, followed eventually by mass production through the printing press) but will not bore you or any other reader with that here.
Finally, you indicate I "presuppose" something can be called "right", or at least better than an alternative argument. Well, yes, but so do those arguing there is an ultimate source of morality out there somewhere independent of our own experience. Only moral relativists would say there isn't, but since I seriously doubt there are any true moral relativists (if we put an innocent moral relativist before a firing squad I strongly suspect he would discover moral objections very quickly) I won't dwell on their flimsy position here. Ultimately, we must choose a definition of morality and any definition we choose will be rooted in very practical concerns about human suffering at a minimum and human and animal suffering at a maximum here on earth. That definition cannot be objectively confirmed on its own independent of the circumstances that gave rise to it. We can evaluate, scientifically and/or experientially how well we are doing at reducing suffering but we cannot prove that reduction of suffering is THE RIGHT DEFINITION of morality independent of any consequences that definition has for us. It may be circular, I suppose, to argue that evolution favours the survival of species that don't love suffering and death and that to the extent a species evolves to become a social animal as opposed to a solitary one it will find a way to exhibit traits like an appreciation for fairness, however imperfectly. I would argue it's just self-evident. But even if you don't accept evolution or accept its role in the development of our moral views, you still have to concede that our creator or whatever transcendent source for morality you choose doesn't favour suffering much either given we can confirm scientifically that those people and cultures who choose it tend to do worse over time than those that find a way out.