We?
'Genetic purity' is not a charitable way of looking at eugenics; how about 'genetic quality'? That's what most of us seek. Nobody asks for a disabled baby.
Should we edit our genes to allow for more diversity? How about all the diverse genetic mutations we haven't dreamed of yet! We could rediscover a lot of weird and wonderful maladaptations that our ancestors have spent millions of years weeding out. We'll have X-Men in no time.
While objective, paperclip count is notorious for not really aligning with our intuition of good vs. bad; I'm pretty sure we can do better. But this illustrates the point that the problem is really about picking from the infinitely many objective measures that, objectively, do already exist.
Humans exist; that is objectively true. Humans have preferences; that is objectively true. Humans take pleasure from some experiences and experience pain from others; that is objectively true, albeit a big simplification. It's objectively true that humans dislike having rusty nails jammed into their eyes. It's objectively true that humans enjoy eating nice meals when they're hungry. We should seek to perform those actions which minimize the number of rusty nails jammed into eyes and maximize the number of times humans can enjoy nice meals when they're hungry. Obviously there are trillions more considerations, but nowhere has subjectivity even entered the picture yet.
What I'm saying is that we can pick, or define, or refine, a truly objective measure; one that is much better than paperclip count. You could say "well there's subjectivity in picking which measure we use " -- only because we have imperfect knowledge of the universe and its future. If we had perfect knowledge of all the likes and dislikes of all humans that will ever exist, all sources of pain and pleasure and suffering and contentment and sadness and happiness, all their values and goals and desires, and how all actions affect all of that, then we could simply integrate their effects over time. Yes, we have to weight them appropriately, and find a good NPV discount rate, and all that, but with perfect knowledge, we could easily find one that's at the very least on the Pareto surface. That's our metric.
So our subjectivity comes from imperfect knowledge. But that's OK -- we accept that we have imperfect knowledge. There's a huge difference between "there's no objective measure of good vs. evil" and "it's really hard to pick an optimal measure of good vs. evil, and to know which actions maximize the net present value of that metric over the course of the universe." The former gives you nothing; the latter at least orients your moral compass toward something that humanity can all work toward together.
Abortion is just one, albeit salient, example. People differ in small ways and in big ways. I daresay your idea of a unified course of action is arrogant.
I was actually careful not to say "moralities" as parameters of the model, because people's claimed moralities are often really awful representations of what they actually want, believe, or care about in life. Nobody is against abortion when their own daughter gets impregnated by a rapist or when it's their own ectopic pregnancy. Abortion is only controversial because it's politically convenient. It's not actually a particularly difficult moral conundrum, which -- again -- you can tell by the fact that everyone is pro-abortion when it's them or their daughter. I don't care about people's stated morality. I care about what actually brings about happiness vs. suffering.
And we should seek to act in such a way that, all else equal, those humans have opportunities to do so, except in those cases where allowing masochists to engage in self-harm ends up causing more harm to others in the long run, e.g. if it emboldens them to torture others or if it causes them to end their own life which would otherwise have been rich and fulfilling for themselves and others. There's no need to generalize to some weird Kantian categorial imperative bullshit here; there's no "lying is always bad", there's only looking at two pairs of actions (or an action and its inaction) and running a net present value calculation on those actions from now until the end of time -- or at least doing our best at this. I didn't say it was easy: it's absolutely not. It's the appeal to a higher power or some bullshit categorical imperative that takes the easy, lazy way out. In fact my moral theory compels us to do a hell of a lot more work and deep thinking than any of the others do.
> While most of us want to maximize our lifespan, soldiers do not. They consider protecting their nations are far more important than their life.
Wow, no, that's not true at all. People don't join the army to lay down their life for their nation, they join the army because in that moment (as a teenager, often in the face of a very convincing recruiter who is loose with the truth), it seems like the best option for their lives.
> we all agree that what soldiers and Mother Terese did is "good."
No, we absolutely do not all agree on this, and "we all agree" is an opener to a lot of bullshit in this world. I don't know Mother Teresa's own internal motivations but the evidence suggests she was a horrible human being who caused a lot of undue suffering. Nor do many people, especially pacifists, agree that soldiers are automatically good people.
> unless, as I said in the previous comment, you're willing to redefine "objective" as the majority's preference
If I allow you to use the shorthand "preference" for the 20 or so measures that I stated (and there are hundreds more), then I'm not redefining anything. These preferences already exist. It'd be nonsense to deny that.
> Which is worse: having 10 nails in each pair of eyes of 10 people, or having 1 nail in either eye of 100 people?
Silly trolly problems get us nowhere. The answer is: it depends on the context. It depends on the people. It depends on whether they were already blind or not. It depends on what the course of their lives would be like with and without those nails. It depends on trillions of factors, and all we can do is do our best.
Luckily, the vast majority of problems we face in life are not gotcha-trolly problems where we have to make these kinds of decisions in absence of literally any other context. In real life, using this framework to orient our moral compass, and then acting roughly in line with that as best we can, will end up with extremely moral people creating a wonderful world for everyone. If we get to the point where we're having to fiddle over the minutiae of utility calculations, then we've already created a magnificent utopia for all anyway.
> There exists something that is an objective measure AND from it good or bad is determined
Yes, I already told you how to do this.
You just keep arguing against what I didn't support or even mention. You were focusing on nonessential details of imperfect examples, which should at least give a glimpse what I've been meaning all this time. Or maybe you really didn't understand of what my counter-arguments really are, after all.
> No, we absolutely do not all agree on this ... Nor do many people, especially pacifists, agree that soldiers are automatically good people.
> ...
> The answer is: it depends on the context. It depends on the people.
The fact that we—and people in general, e.g. pacifists you mentioned—don't agree what's moral or not just proves my point that it's probably impossible to define objective morality from physicalists' point of view. As I've said many times, the closest thing to objective morality is a concept of good or bad based on whether it's beneficial for survival or not. But even this, as I explained in other comments, has its own problems.
There are many other things that evolve too: ideas, memes, viruses, and many more if you relax "evolution" to simply mean "progress", like my own knowledge and the capabilities of the human race. It's myopic to focus on genes alone.
> eugenics
Eugenics takes for granted the idea that some "genetic purity" is good for its own sake. Why? Why is a world with fewer, but "genetically superior" people, (and more genetically similar), better than a world with more people and more genetic variety? That's not even necessarily good even if you myopically focus on the actual gene pool, much less if you take all the other aspects of humanity into account.
> So, how exactly do we know which is good, which is bad? Is there even an objective good or bad without invoking the idea that some higher beings say so?
Yes, there is: we all collectively decide properties of the world we'd like to live in, and we try to guess what kind of world future generations would also like to live in, and then we call those actions that ultimately improve those properties "good" and those that lessen those properties "bad", and we can even partially rank actions based on the integral of their effect on these properties from now until the end of the universe (allowing a Net Present Value calculation to avoid infinities, to acknowledge our imprecision of future outcomes and preferences, and even to simply prefer utility now over the same utility later). We try to maximize happiness (in its various forms, some more important than others) and minimize suffering (ditto), taking diminishing returns into account so we don't just make one dude trillions-happy at the expense of everyone else. This has infinite degrees of freedom and requires perfect knowledge of the future, so we know it's not actually possible to achieve, but it gives us a direction to orient our moral compasses and strive to get as close to this perfection as we can.