Here is a reply on the substance of your arguments.

Let's address the substantive points you've raised here. In order, these are:

(1) Is marginal utility even a "theory of value"?

You point out here that marginal utility is a theory of price but not a theory of value. To this I have three replies.

1a: Fair point, but this doesn't mean that Marx's conception of LTV is correct, or that LTV is correct. Since the LTV is woefully broken in predicting price in pretty much any realistic scenario, and Marx casts value in terms of price, none of his arguments have premises that are supported in a meaningful way. So maybe we don't have any workable theory of value--maybe there isn't one because there is no coherent conception of "value" of this sort. But even if we decide that value does have a coherent meaning and therefore there ought to be some theory of value that explains it, it doesn't follow that we should use LTV. It's so wrong that it's more likely to mislead us than to provide insight.

1b: Menger did cast marginal utility as a theory of value. I have a vague hunch that it ultimately was not persuasive as such because it shared too many flaws with Marx's conception (in something akin to use-value--that is, what comprises an economic good--that is rather hard to support robustly). Nonetheless the key insight was that it is people's desire for things that is causal and the labor follows (in an efficient market)--desire for that which is (perceived as) better is the source of value. If LTV is, despite unsound justification, allowed to count as a theory of value, Menger's conception has also to be able to rescue marginal utility as a theory of value.

1c: As a general theory of value, LTV, whether in Marx's conception or anyone else's, is extraordinarily deficient. There are many things that we value (social acceptance, a beautiful view, etc.) that cannot be reduced to an equivalent amount of simple labor, for instance. On the other hand, as a theory of economic value, Marx's conception of LTV is also extraordinarily deficient because a the very least a theory of economic value had better be able to at least account for price.

(2) You claim that social utility plus the law of supply and demand fixes the grass bouquet problem, and claim that Marxists do not think that inputting labor magically causes something to have value (which is what grass bouquets are meant to illustrate is wrong).

The problem with this point is mostly that Capital seems to contradict it (but also, it offloads all the heavy lifting to marginal utility, and then assigns credit in the wrong place).

If we use the text at https://content.csbs.utah.edu/~ehrbar/cap1.pdf, we can see places where Marx explicitly was not leaning heavily on supply-demand curves (1.1, page 18): "The introduction of power looms into England probably reduced by one-half the labor required to weave a given amount of yarn into cloth. The English hand-loom weavers, as a matter of fact, continued to require the same time as before; but after the change, the product of one hour of their individual labor represented only half an hour's social labor, and consequently fell to one-half

its former value."

No consideration of capital outlay, no consideration of market elasticity, no rebalancing of the equivalence of

yards of linen with coats and tea and so on (1.3.C, p. 109), no consideration of cost of raw materials, and so on. If Marx had explicitly said he was considering the case where instantly everyone could trade in their hand looms for power looms, etc. etc., then the magical labor-input view would not be the most natural interpretation here.

Indeed, Marx's justification for labor as the thing-in-common between commodities that sets their relative prices is both empirically wrong and absolutely necessary for his argument demonstrating that labor is ultimately the source of value. If you keep pressing on "socially necessary" until you actually get a workable theory of prices, you end up with...marginal utility. At which point there is no justification left for labor being the thing in common even between commodities.

So, anyway, you might be right that social necessity rescues Marx from the grass bouquet problem, but in so doing it also destroys the labor theory of value: instead, it's a theory of "go read the answer off of marginal utility, wait for market stability, and then mis-assign the credit to the amount of labor rather than how much better people think a thing will make their lives". (Marx's distinction between simple and complex labor gives all the wiggle room needed to defer fully to another framework, leaving zero explanatory power with LTV.)

(3) You describe a scenario where the cost of gasoline is largely irrelevant to someone's plans, but I can't see how this is relevant to the discussion--I was making a point that you can't solve the grass bouquet problem by declaring that it has no use-value. I was responding to an objection...and I'm not seeing how your counterargument counters my response. If it doesn't, I'm not sure what it's for.

(4) You commit a logical fallacy by suggesting that things other than Marxism have flawed premises. No need to address this.

(5) Presenting quotes is a type of appeal to authority (sometimes socially useful if logically irrelevant to the argument); you incorrectly charge the poisoning the well fallacy when I (with amusement) questioned the credibility of the authority of the source of your quote. I was assuming that the authority was being used for its social purpose (i.e. this is one of the key people--pay attention!).

(6) You acknowledge that there are myriad cases where Marx's canonical example fails to hold. We agree!

(7) You introduce the term "overdetermined" to mean "model doesn't fit the data a lot of the time". Fine--call it whatever. The question is how good of a job does it do at explaining things in comparison to other models. There is no difference here between social sciences and other sciences.

(8) You point out that Adam Smith also believed in the labor theory of value. This does not rescue Marx's argument; it just makes Smith wrong in that way too.

(9) You charge that I didn't get to a point.

Okay, granted, I was leaving some things unstated that maybe I should make explicit.

A labor theory of value needs to ground value specifically in labor, not in other things, or it is not a "labor theory of value". At best it's a labor-containing theory of value.

If labor intrinsically has value, then you are forced to say that the labor that goes into making grass bouquets is as intrinsically valuable as any other sort of labor, even though the market price for grass bouquets is probably zero in almost every case where you just randomly decide to start making them. My example points out that equating any random labor with monetary value is incorrect.

This leaves us with two options. You could embrace that, nonetheless, labor has value, but reject the idea

that the sort of value that labor has is an economic value. Rather, it could be a moral value. Alternatively, you could reject the idea that labor is the source of economic value in a meaningful sense, although in some contexts it obviously plays an important role in constraining supply and setting prices when labor is limiting.

My charge is that as an economic theory, Marxism is rubbish. It's not a matter of being overdetermined; it's that Marx, like Smith, got wrong what the causal factors were, leaving him to have a strictly less powerful model compared to marginal utility theory. It is akin to deciding that it is the orbiting of one celestial body about another that generates gravity. So, for instance, the orbiting of the Moon around the earth gives Earth its gravity--you can't tell the difference normally, but any time a situation comes up where you can (satellites, transiently captured moons, etc.), you realize that it's completely backwards or come up with special-case laws (satellites are too small, transient capture doesn't count, etc. etc.).

As a matter of morals, I think that a labor theory of value is not rubbish. Or, rather, an effort theory of value. If you put effort into something, it behooves others to treat your effort as if it is of value to you. But here too, it's an incomplete theory of value: not everything seems easily reducible to effort, and attempts to do so seem to miss the underlying causality. For instance, affection for a romantic partner is not easily reducible to one's effort in having found them.

So, grass bouquets illustrate that labor does not intrinsically possess economic value. Price won't naturally gravitate towards it just because there was labor involved. Rather, labor may gravitate towards places where high prices can be commanded (because people like money). If you want a labor theory of economic value, you first have to use some other theory of economic value to calculate what the economic impacts are. For instance, if you have farmland of differing soil quality, you can use supply and demand curves to estimate how much farmland overall will be put into production, recognizing that profits will be greater on the greater-productivity land. Then you forget all that, assign all the credit to fixed-value labor, and give yourself a gold star for cleverness.

So as it stands, Marx's conception of the labor theory of value is not fit for any purpose. It is too narrow to be a theory of moral value, and it has no ability to predict economic value aside from deferring to other theories that actually give the answer.