Part of the answer to your question is that fictional objects don't exist: in that sense you don't create them. What you create is a kind of specification, like 'a person who knows all the laws of physics'. The specification is real, but there is no real person who fits it. But this isn't the whole answer, because even though we can't create something just by specifying it (or else we would all be rich), it can still seem mysterious that we can even specify a person who knows something we don't know. How can we even come up with the specification in this case? But that is a cool thing about specification: there is a sense in which you can specify a fact you don't know. I don't know the score of the last Red Sox game, but I have no trouble specifying that score: I do it simply by means of the expression (or thought) 'the score of the last Red Sox game'.

Thomas Kuhn goes some way in this direction in his work on the nature of science. (You might have a look at his classic Structure of Scientific Revolutions , especially chapter ten .) It's not that he denied that there is an external world that sharply constrains what scientists can say; but he did hold that the structure of kinds and properties that scientific theories ascribe are not out there in the world independently of us but are something that the scientific community imposes on the empirical reality it is studying. Like Kant, Kuhn held that the empirical world is structured by the minds of those who study it. Only where Kant thought that the structure contributed by us could only take one form, Kuhn held that the human contribution changes with each scientific revolution. Thus Kuhn is Kant on wheels.

The most compelling reason not to eat meat is not because it involves killing animals but because it so often involves causing animals to suffer, especially in factory farming. From this point of view there might be nothing wrong with eating free range chicken (because their lives are not miserable) or shrimp (if they are incapable of feeling pain). But as Peter Singer argues, causing unecessary suffering seems wrong. If some factory farming were the only way for some people to get enough iron, then it might be a tough call. But I doubt it is, and if I am wrong about this the argument still applies to many of us who do have easy alternatives. And causing unecessary suffering seems wrong even if the perpetrators are acting perfectly naturally.

I agree that sight and indeed the senses are our anchor to the physical realm, but I think that is a good thing, since the physical realm is what we need to understand. At the same time, our senses give us only very limited contact with the physical world, much of which is unobservable. Creatures with different senses might have a cognitive advantage over us in this respect. But any sort of physical sense we can imagine (such as echolocation in bats, or exotic sensory sensitivity to chemicals) would still require massive inference from the limited effects of the world the experiencer to the complex worldly causes of those effects. At the same time, science has done an impressive job of reducing the limitations stemming from the peculiarities of the human sensory endowment through the construction of instruments that enable us to detect things we cannot directly observe.

When we see or otherwise represent the world outside our minds, the act of representation is different from the object being represented. The object represented, say the Eiffel Tower, is something physical, but the act of representation is a thought -- something mental. This difference between that act of represenation and the object being represented might seem to entail that all representation introduces bias. The idea is that the act of representation must introduce something foreign to the object being represented, since the act is different from the object. But this is a bad argument. Of course there is no thinking without thinking; but it does not follow from this that we can only think about thinking, or that thinking always infects what we are thinking about. Just because the act is mental doesn't mean it represents the object as being mental. A postcard of the Eiffel Tower is flat, but it doesn't represent the Eiffel Tower as flat. Seeing the Eiffel Tower is a mental experience,...

Best for whom? The enviroment may change so that a particular species of tree is no longer very successful at propagating itself. If we do nothing, it will go extinct. But it might be much better for us if we did not let that happen, because the bark of the tree contains a chemical that is highly beneficial to us.

Your question raises a number of interesting issues, but I will here just ask one brief question in return. If we were more victims of our environment than of our genes, could we then truly be held culpable for our misdeeds?

Here are just a two brief reactions to your good question. First of all, maybe we do have an infinite number of beliefs. I believe a have fewer than three arms, and that I have fewer than four arms, and just maybe I believe that I have fewer than x arms, where x is any integer greater than two. But that is an infinite number of beliefs. Second of all, there can be belief that p without a belief that there is a belief that p. Dogs are good examples. Fido believes that there is food in his bowl, but he doesn't believe that he believes that he has food in his bowl, because he cannot entertain a thought like that. Dogs have beliefs, but they don't have the concept of belief. Perhaps people are like that two. Sure we, unlike Fido, can entertain the thought that there is a belief that there is food in the bowl, but maybe when you iterate the belief operator beyond a certain number of times, we lose conceptual grip.

There may be a debate over whether spacetime is continuous or granular: I will have to leave that to others. But there seems to be a problem with saying that a diagonal line is a microscopic staircase. If it was, then the diagonal of a one inch square would be two inches long, when in fact its length is the square root of two.

You are right about proof. No scientific prediction can be proven from the scientific data, since it always remains possible for the data to be correct yet the prediction mistaken. The same goes for scientific claims about unobserved causes in nature. But it doesn't follow that we have no reason to believe these claims. I can't prove that my keyboard isn't going to burst into flames in the next minute, but I do have reason to believe that it won't. Admittedly, the great David Hume gave an argument that we have no reason whatever to believe that my keyboard will remain unignited for the next minute, but the fact that scientific claims are not proven still does not in itself make them any more speculative than my belief that I'm not going to burn my fingers.