i don't see why the assumption should be it's more likely for whatever your constitution's drafters thought was basic rights to be good shit and not "marriage is between a man and a woman", "any expropriation or taxation whatsoever of property is illegal", "freedom of association extends to businesses having the right to discriminate against applicants/employees based upon their gender or skin color", etc
I don't understand what this ask is actually about. Constitutions aren't fixed and immutable documents, and even if they were originalism is a stupid legal philosophy--there's a reason it's been partially abandoned even by the right-wing wackos who originally propounded it (though its successor, textualism is even worse).
The problem is that textualism is obviously correct but extremely limited, and thus Textualism is pretty stupid. (Honestly you can say something similar for originalism, but not quite as clean-cut-ly.)
Like, sometimes the text is extremely clear. And there's a ton of value in the idea that we follow the actual law that's written, rather than what we wish it were. As with the example everyone always points to, no one would say "oh they didn't really mean you can't elect a 34-year-old president, that was just a metaphor for how we should respect experience" or whatever. And in that sense, some form of textualism is correct.
But Textualism as an interpretative school is dumb, because there's no such thing as perfectly unambiguous language. So your interpretative philosophy can't just be "do whatever the text says". Essentially every philosophy says "do what the text says when that's clear"; the question is what you do in the gaps.
(Some approaches do in fact say we should just ignore the text when it's inconvenient. They are bad.)
And then of course Textualists have the second problem that sometimes the text is inconvenient and so they read it in bad faith to get the result they want, but I think that's better read as a criticism of the people than the abstract philosophy.
I mean, to the extent that one might characterize legal realism or some other legal philosophy as "oh they didn't really mean you can't elect a 34-year-old president, that was just a metaphor for how we should respect experience", I do not think this is an accurate characterization of any legal philosophy. And to the extent that by small-t textualism you mean "if it were possible to accurately and exactly determine the generally-understood meaning of a law at the time it was enacted, we should definitely use that understanding of the law" that is also really stupid. As in, "such a bad legal philosophy you could not even begin to run a country that way."
Like, to take the 2nd amendment as an example; let's grant for the moment that DC v Heller was correct in saying that the 2nd amendment concerns an individual right to bear arms (this is incorrect by textualism's own criteria; another big problem with both textualism and originalism is that judges are not trained historians, and are lousy at the kind of historical analysis that both philosophies would require; also, the conservative judges who use textualist arguments are especially dishonest in their application of the historical research they do perform. You can say "oh, this is a problem with the people using textualism, not the philosophy," but if everybody who proclaims a philosophy is using it manipulatively, I do not think the difference between the people and the philosophy is a very substantial one). "Arms" in 1791, as a category, cannot apply to things which do not exist. Many, many weapons have been invented since then, some of a category completely different to anything imagined in 1791. All law has to proceed on some degree of analogical reasoning; a modern rifle is very different from a firearm in 1791, but it sort of vaguely resembles one. But an atomic bomb? An attack helicopter? A recoilless rifle? A tank?
At a certain point, whether narrowly or expansively, we have to decide whether a law is aimed at general principles or is meant to be narrowly applied, and in a lot of cases I think that is an argument which small-t textualism alone cannot answer. The US is pretty good about keeping records of debates on laws (but note that textualism is not about the drafter of the law's intent; that's originalism, and originalism has become unpopular precisely because we often have records of Congressional debates that flatly contradict modern conservative legal movement dogmas, ergo the shift of the goalposts), but law is not mathematics or computer programming, and legal processes simply cannot function in a purely mechanistic fashion. I'm skeptical about whether that would be desirable anyway; but whether they should or not is kind of philosophically moot, because that's just not how law works.
Insofar as law has to be a useful Schelling point for actually-existing societies, a pretty big degree of non-small-t-textualist legal philosophy is necessary to produce useful decisions. Fortunately for a lot of simple stuff like "how old do you have to be to be President" the gap between small-t-textualism and other kinds of jurisprudence is essentially nil. Unfortunately, the complicated questions are occasionally really consequential!
I think you are agreeing with me.
By small-t textualism, I mean "to the extent the literal written text of the law admits only one interpretation, we should interpret it that way." Which is why my leading example was the age cutoff for the presidency. As you say, essentially no one argues over the interpretation of that rule, because arguing would be fucking stupid.
The problem is that, as you say, this just doesn't get you very far. Small-t textualism is correct but isn't sufficient to produce a ruling in most cases, and so it's not really a philosophy so much as an observation or a constraint on the philosophies you choose. Large-T Textualism is implicitly a claim that small-t textualism is nearly-always sufficient, and thus large-T Textualism is wrong.
But note that small-t textualism isn't the same thing as originalism either. (There is a similar thing I could say about originalism; if there is a clear answer to what the law was intended to do, you should probably read it so it does that. See e.g. the Religious Freedom Restoration Act; it was passed more or less explicitly to overturn a specific SCOTUS statutory interpretation, so you pretty much gotta interpret it to do that work.)
But like if, counterfactually, the second amendment had included the text "every citizen shall have the absolute right to own firearms of any sort, which the government shall not infringe in any way", then maybe that's a bad amendment but it would be disingenuous in the extreme to read that as not protecting the right to own a submachine gun.
Eh... If that were the case then the left would be taking the originalist position that "firearms" has to be understood as the framers did, which evidently doesn't include ones using smokeless powder.
Also that amendment would not obviously protect knives or other blades, nor batons and suchlike, as the OTL version does. Nor nuclear weapons which are presumably not "fire" arms, they produce heat by entirely unchemical means.
First, sure, people always will make bad-faith arguments, but that argument would be obviously bad-faith in a way the arguments about the actual second amendment aren't.
(My favorite obvious-bad-faith argument is the series of decisions that Congress doesn't have the power to pass various laws intended to give teeth to the Fourteenth Amendment, despite Section 5 of that same amendment.)
Second: yeah, not protecting nuclear weapons, or even artillery or cannons, was an intentional aspect of the way I wrote my hypothetical. And I wasn't consciously intending to exclude knives from my text, but I agree with you that I did; and that's sort of my point. If that were the text of the constitution, I think courts would be essentially forced to rule that you can't regulate submachine guns but you can regulate knives if you want to. That seems like silly policy but that's an argument for changing the law, which sometimes is what it is.