I see nothing unnatural about a bird that can run or swim but not fly. Yes, trying to say what a bird should or shouldn't do based on any definition of a bird would be stupid, and that same principle applies elsewhere also, even though people do it all the time. It is to some extent an unavoidable stupidity though, because thinking about things at all usually requires making some simplifying assumptions, conscious or otherwise. I try to remain aware of my working hypotheses, and avoid hardening them into judgments beyond what is supported by evidence.

Yes, moral problems are both over and under-determined. One consequence of immoral action is it creates conditions in which avoiding further immoral action is impossible. And we were all born into such conditions. That's what I mean by over-determined, there are moral contradictions built in to life that we can't solve. By under-determined, I mean that we have some freedom of action that is not discernably more or less moral than other action. The fact that we have some freedom to make reality doesn't mean that we can make it into anything we want to though, because our ideas of what we want often aren't internally consistent and completely consistent with how nature must work, which we have limited understanding of. That's what I meant when I said its not arbitrary. To use your analogy, if there are other constraints on y, and there pretty much always are, then some choices of x will allow a reasonable solution and others won't, even though that might not always be obvious when the choice is made.

I don't define morality strictly as being what a person should or should not do. I realize that puts me at odds with a lot of other people's definitions, and I should try to conform to other people's use of language to the extent possible. But if a more common definition assumes there is always a 'right' course of action, then I can't think that way, because I don'[t think that's true. Suppose a person does something that's "wrong", but they don't know it is wrong. Is it then not wrong, because they don't know better? If horrific results follow as a consequence, the action is still wrong in that sense. And they may still carry a lot of responsibility for cleaning up the aftermath of what they did, even though they can't be expected to have made a better choice.

For me morality is only weakly a matter of ethics. Following agreed upon ethical rules has moral value, but it frequently gets trumped by more substantial moral considerations. If your argument is against the primacy of ethical rules, then we're on the same page about that. To a significant extent, my moral yardstick is empathy, tempered by objective honesty and a willingness to accept difficult truths. I realize that's a subjective and imperfect yardstick, but that doesn't make it completely arbitrary or useless. There's also an element to it this that involves an appreciation of beauty, and being able to intuitively anticipate future consequences that can't be analytically extrapolated from present actions. When I say that morality isn't strictly a matter of what a person should or should not do, what I mean is the essential thing is the sincerity. It may be possible to act in a way that avoids harm, or it may not be, and in either case we need some freedom to do what we want. But we nevertheless have some responsibility for what we do.

In regards to evolution, I see natural selection as an important aspect of how nature works. It is a constraint that needs to be satisfied. If something isn't capable of persisting to exist beyond some point, then after that it doesn't exist. Natural selection doesn't fully determine outcomes though, there are a lot of alternative paths that are equally 'fit'. A common assumption is that to the extent that natural selection isn't causal, everything is random. There is the cause we can potentially manipulate, observe, and model well enough to describe scientifically, and everything else is arbitrary. I think that perspective is a philosophical choice, and that it is incorrect. I think that luck isn't entirely random. I have enough evidence in the form of personal experience that I think I can say I know this, though demonstrating it to another person can be problematic, and demonstrating it in general to a large category of people would be even more problematic. I think that the nature doesn't work entirely through the passive or negative constraint of natural selection, combined with the positive impetus of random perturbation, even though randomness is important also. It isn't enough. I think that to some extent a bird that can fly is able to because it was meant to fly, and because it wanted to fly. There are outcomes we're being dragged towards, we're not just drifting forward from the past. A poster in this forum a few years ago suggested this works through quantum entanglement, which operates temporally as well as spatially. I didn't find that argument very convincing, but I can't refute it either. In any case, even though the mechanism is outside my understanding, I think there are things that are likely to happen in the future that aren't likely as an extrapolation from the present in terms of physical causes. And I think that this is a part of evolution.