Regarding 2 and 3, do you mean that anyone can choose whom they consider mentally ill / a deviant? If so, doesn’t that make arguments about the issue pointless, because everyone will decide to define it differently? That’s a kind of postmodernism / pluralism without one objective truth, because there are no arguments. It’s up to my decision, and that’s it.

First, this is not a matter of arbitrary decision but of opinions. Do you think left and right are arbitrary? So what would be the point of arguing about them? Everyone has his own view. You can argue about opinions too (I’ve explained in several places that this is the essence of rhetoric, as distinct from demagoguery).
Second, there are concepts that really are devoid of objective content, and about those there truly is no point in arguing. Argue whether some phenomenon is permitted or forbidden, desirable or not, but there is no point in arguing whether it is a disease. For example, is there any point in arguing whether so-and-so is tall or short? It depends on where you draw the line.
The fact that there are such concepts does not take us into postmodernism. Postmodernism is the view that all concepts are like that (relative, so there is no point in arguing about them).

So the discussion of permitted/forbidden is binary, while the discussion of tall/short is continuous? What is the conceptual difference between those terms?

The point is that tall-short is a relative matter (not necessarily continuous), and therefore it is not well defined unless you have set a reference line.

Is stealing two shekels more forbidden than stealing one shekel, or is it all the same?

I don’t see the connection to our discussion.
As for the question itself, it seems to me that there are two laws here: the prohibition of theft is the same prohibition—taking something that is not yours without permission. However, the consequences for the other person can be more severe, and therefore in the sense of harming him, there is a more severe prohibition in taking two shekels. But that is not the essence of the prohibition of theft, but perhaps “love your neighbor as yourself,” and the like.

Sorry for the nagging, but I feel like I still haven’t exactly grasped it. Why is relativity not identical to continuity? In ideas involving the taxonomy cow/donkey, if there were another thousand intermediate creatures in the world along the cow-donkey transition, would you say there is an absolute donkey pole and an absolute cow pole, and that deciding where to draw the line is pointless, like with tall/short?
With theft too, you can make a scale of levels of ownership. For example, if someone sees ownerless property, when does it become his—when he sees it, when he declares that he wants it, when he starts running, when he is within four cubits, when he touches it, when he moves it, when he lifts it, when he uses it? It’s not clear to me why here there is a sharp and clear line from which there is an absolute prohibition of theft and before it complete permission, whereas in other essential concepts it is not so. Not a sharp question—I need to think more—but maybe the answer will still clarify it.

When you ask where the line of the prohibition of theft lies, that is a normative question, and one can Definitely say that it has a correct answer (even if there are disagreements about it). It is also a question of placing a line on a continuum (the sorites paradox).
Here I am asking you where, in your opinion, the line of prohibition lies.
But the question of whether something is a disease is ostensibly a factual question, but in fact it is empty of content. You can ask whether these things are permitted or forbidden, but not whether they are a disease. This is not a question of a continuum and the sorites paradox. There is no black here (something that is certainly a disease), and perhaps no white either (something that certainly is not a disease. Although here one might say that a normal person who suffers from nothing is certainly not ill. But even about that one can quibble).
The question of whether someone is tall is also not a problem of a continuum but of a relative determination. It is not exactly the same thing. Thus, for example, one could formulate it on a discrete height axis, and even there I would tell you that it has no meaning.
I do not understand what is unclear here.

To tell the truth, I also don’t know what is unclear to me.
A. A norm is an idea like any other idea. If you can draw a line for when the norm begins, then you can also draw a line for when the idea of height applies.
B. And if I ask a normative question about disease—who deserves public funding for medication (let’s say it is agreed that the public ought to fund medical help for the sick)—then suddenly it would be possible to define disease? Every norm depends on a factual substrate (just as theft depends on the definition of ownership), so it’s impossible to distinguish between norms and facts-metaphysical facts; rather one must distinguish between kinds of metaphysical facts.
I won’t ask more before I think.

(For that matter, by continuous I also meant a discrete axis. The main thing is that one has to draw a line, whether it is continuous or not. Although it seems to me that on a discrete axis there is always continuity too.)

Not true. If you tell me for what purpose you want to define height, then one can talk about the location of the line. That is exactly the difference. To discuss whether someone is tall without saying in what respect or for what purpose is an arbitrary and meaningless discussion.
Of course, even if you tell me for what purpose you need the definition, it is not certain that there will be a Absolutely answer, and even less certain that it will be agreed upon. But here the discussion has meaning.
As for your assumption that every norm depends on a factual substrate, that is true. Still, sometimes there is no point in discussing the factual substrate outside the context of the norm. On a similar matter, I only just now finished an interesting discussion with a doctor about determining the moment of death. He argued that one must begin the normative discussion (about harvesting organs and so on) from the factual determination, whereas I argued that the factual determination is an empty discussion. Only after you tell me for what purpose you are interested in that definition will it make sense to discuss it (and even then we will not necessarily reach conclusions, and certainly not agreed-upon conclusions). There it does connect to continuity, but my feeling is that not really. The problem is not where the line runs on the continuum, but that there is no such line. The line is context-dependent (normatively). Note this carefully.

Thanks

You reminded me to upload that correspondence to the site. So I uploaded it. Here it is:
https://mikyab.net/%D7%A9%D7%95%D7%AA/%d7%a1%d7%95%d7%92%d7%99%d7%99%d7%aa-%d7%94%d7%92%d7%93%d7%A8%d7%AA-%d7%B4%D7%90%D7%93%D7%9D%D7%B4-%D7%95%D7%B4%D7%9E%D7%95%D7%95%D7%AA%D7%B4-%D7%91%D7%99%D7%94%D7%93%D7%95%D7%AA#answer-71996&comment=52797