1. It’s not the fact that the Jewish people accepted the Torah upon themselves that obligates you. God, by definition, obligates you to obey Him. Acceptance of the Torah is only an indication of what the content of His will is.

2. The laws of the Israeli Knesset do not have formal authority in the sense being discussed here. We are obligated by them only by reduction to arguments of improving society / order / preventing anarchy, etc. Laws that are pointless and certainly not beneficial, or are harmful, do not obligate me; a Knesset that legislates laws that are "manifestly illegal" would not obligate me.

3. Are you claiming that one need not arrive at the consideration that my people accepted this upon themselves such-and-such years ago, but simply that it is reasonable that this is what God wants given that there is no Sanhedrin?
If I understood you correctly, that is not a pragmatic consideration, but it still doesn’t seem very convincing to me. It’s hard to know what God would want in such a situation. What would Judaism look like today if the formal obligation to the Talmud were to stop today? (Even if there were excellent considerations for Jewish survival in accepting such authority in the past, I’m asking a specific question about today.) Maybe that’s what God wants?

This requires a longer answer, but it’s the eve of Passover so I’ll be brief.
In Column 457 I distinguished between the content of morality and its validity. I wrote there that its content is binding even on the Holy One, blessed be He (like logic), but its validity stems from His command. I don’t remember, but somewhere I showed that this distinction also exists in Kant, and that resolves the difficulties his interpreters raised about the apparent contradiction in his words regarding the need for God in order to validate morality.
Similarly, in Column 679 I distinguished between the severity of the prohibition and the validity of the obligation to observe it. The claim is that a rabbinic prohibition is less severe, but the obligation to observe it is exactly like a Torah prohibition.
Similarly, one should also distinguish regarding halakhic obligation. There are two different planes of relating to it: 1. Why it is proper to do it. 2. Why one is obligated to do it. It is proper to do it because it is the will of the Holy One, blessed be He. The obligation is because we signed a contract/covenant with Him. Without the contract, someone who does not comply is acting improperly, but no claim can be made against him. He was not obligated.
Think of a person who was in the Gaza-envelope area on 10/7 and took no action to save people (let’s say he could have). That is morally reprehensible, but he was not obligated. No claim can be made against him, because a claim requires obligation. By contrast, a soldier or officer who did not do his duty to save people can be held accountable, because he had an obligation. The difference between them is not on the moral plane, since morally both should have acted. The difference is legal, in the aspect of obligation. A soldier has an obligation and a civilian does not.

Regarding the laws of the Knesset, I think we’ve already argued about this. I disagree. There is an obligation to obey by virtue of the fact that I chose them. True, I did so and agreed to give them authority because it is proper to maintain social order, but that is only the rationale. It explains why it is proper. Once I chose and signed, I am also obligated to obey them. Laws that are manifestly illegal absolutely do obligate us, except that standing against that obligation will be a moral obligation, and in extreme cases it will override the legal obligation.

I really appreciate your answer on the eve of the holiday! Feel free to reply after the holiday, of course:
1. From God’s very will I feel obligated, not just that there is a moral value by virtue of God’s very definition (Cain was held accountable for murdering Abel even though he didn’t make a deal with God accepting upon himself not to murder).
2. Even if I accept your distinction, why does what my ancestors did 1,500 years ago (signed a contract to accept the Talmud as authority, some of them, not all the Jews) obligate me today? Same regarding the laws of the Knesset—why do those human beings who signed a contract back then obligate me? I understand that you see this as a binding value and I don’t. I’m asking whether you have some rhetorical way to show me, like another example from life (the Knesset laws don’t convince me). I also dare claim that this does not convince most of the believing public either, so they are “covert” deniers of Talmudic authority.
3. According to you, without divine revelation it would not be possible to make claims against a person who behaves immorally?! Assuming of course that I also believe in God and that the validity of morality comes from Him. Do you need the Torah? The Torah is infinitely plastic, so it seems it cannot help at all.
I certainly do have a claim against a person who walks down the street and sees someone in distress and does not help him (let’s say there is really no cost to helping him and no danger), even if he did not make a covenant beforehand

4. Even if there was some agreement between Jews and God 1,500 years ago that they accepted the authority of the Talmud upon themselves, that would be a figment of their imagination. God is not part of that agreement. So how does that obligate me? Did they make an agreement with future generations? I don’t see how this argument holds water

1. Indeed, a moral obligation. That is what is proper. Even without a command, there is obligation by virtue of the fact that this is what is proper. Cain was not held accountable halakhically or legally, but morally.
2. You are an individual within the public, and when the public decided, that is considered as your own decision, and you are bound by it. This is the explanation both in law and in Jewish law.
3. Of course it is possible. You don’t need revelation, but you do need to know that this is God’s will. And indeed, the content of morality is not learned from the Torah. Its validity can be learned from it (“and you shall do what is upright and good”), although you do not need the Torah for that either (there is conscience and reason, as with Cain).
You do not have a legal claim against him, only a moral one. The law and legal systems have no claim against him.

🙂 There is no agreement whatsoever with the Holy One, blessed be He regarding the Talmud. Where did you get that from? The agreement with Him was about the Torah. I brought that as an example that social agreement binds the future individual. And so it is also regarding the Talmud.

What if the social agreement contradicts other principles? For example, if there is a commandment to count and offer the Omer sacrifice on the day after the Sabbath, and as a result of a social agreement to obey the rabbinic interpretation, these things are done on the day after the first festival day, then it turns out that the social agreement uproots the command from Sinai, which is also proper and was also socially accepted as something to obey (as you wrote here). Presumably you are not claiming that Israeli law is capable of uprooting commandments of the Torah just because it enjoys social agreement.

Then it is likely void. The public accepted something, and it is supposed to uphold the contract it signed.

If so, are you careful to observe shofar and lulav when a festival falls on the Sabbath?

Absolutely

For a completely atheist person, would you expect formal obligation to the Talmud simply by virtue of the consideration that he is part of a group that once accepted this authority upon itself? I’ll allow myself to assume that even you agree this is not a convincing argument for atheists. So why should it persuade a believer who believes all the facts that you believe (naturalistic fallacy)?

Absolutely not. Clearly there has to be substantive logic behind this acceptance. If one does not believe in God, there is no reason in the world to keep a foolish system of laws just because some group accepted it upon itself.
The difference between a believer and an atheist is not only with respect to facts (whether God exists and whether He commanded), but also on the question whether His commands obligate and whether they are beneficial/correct. So the naturalistic fallacy is irrelevant here.

Suppose I accept that His commands obligate and are beneficial. He did not command me to accept the formal authority of the Talmud. Therefore it is not beneficial for me to accept such formal authority upon myself. So I ask again: why should I be persuaded to accept it because at some point the social group to which I belong accepted it?

I said there has to be substantive logic, but not necessarily a command. For example, in state law the logic is maintaining order, and therefore one obeys the law even if in itself it does not seem right to me. The same applies in Jewish law: one obeys the law even if it does not seem right to me. But that is only for someone who accepts the general principle of the framework—that these laws are to be upheld.

Suppose you lived in the 17th century in some town in Poland with all the knowledge you have today, and the local halakhic authority, whom the whole community had accepted upon itself, ruled for you nonsense and absurdities (not the sharpest pencil in the box). Would you act according to his ruling because he has formal authority? If not, what is the difference between him and the Talmud? And if he were a Torah scholar, would he then have formal authority over you?

If there is demonstrable nonsense in the Talmud, I would not do it. As for the community, I can of course leave it. But as long as I have not left, I am bound by his rulings unless they are utter nonsense. In general, a rabbi’s rulings apply to the public domain, not inside my private home.