The "value is subjective" meme is just lolberts sticking their head in the sand. If you accept that totally and that there is no rhyme or reason to value, then you can't make any meaningful conclusions from that one way or the other. It's a way to absolve themselves of having to debate actual meaning and resort to pre-planned talking points about their feels.
That said, in a way value is subjective, in that it only matters so long as human beings engage in exchange and invent some system of equivalencies for various goods in the market or when bartering. But, once you enter the realm of production, there are definite, material, and real factors in that production which cannot be handwaved away, and one thing which is fundamental to all commodities is that they are the product of human labor.
Why human labor? Ultimately, it's because most of the people in capitalism are working for a wage in some form, and that is what binds them to the economic system in the first place. One of the uses of money is ultimately to command labor and guide people to do what the owner of that money wants. Money, of course, is not inherent to the universe or human nature, and the very existence of money is a subjective fiction we all agree to, yet almost everyone alive doesn't have to a choice to not participate in the money economy in some way, and even if they don't use money themselves their lives are determined by money (for example someone living in an assisted living facility has a definite cost associated with his upkeep). There is simply no real, material basis to compare goods in terms of exchange value, qualitatively they are different things, but we as people make exchange calculations for our own reasons and once we do those calculations have to be based on material reality to mean anything. Shouting at the top of your lungs that value is subjective, then, is just a kind of economic autism.
I think some socialists get it wrong when they talk about workers "getting the full value of their labor". When Marx talked about economic exploitation, he wasn't decrying a mean thing capitalists do and his observation was not novel. Marx explained exploitation and surplus value as necessary steps for his critique of capitalism, and explained exploitation as a necessary condition for capitalism to perpetuate itself. This was not something that was a novel revelation - everyone who has ever worked for a living and anyone who had to pay taxes to someone above them knows how this system works. It was only in the minds of the most vulgar of economists that this even needs to be questioned.
Any socialist system sufficiently advanced would have to move beyond exchange value and look at the qualities of the goods being produced, then allocate them based on use-values (that is, the effects of the goods in question and the desired outcomes). I believe we could do this partially now, and work out a scheme for compensation in labor vouchers as a temporary measure to function kind of like money, until such time that people are accustomed to dealing directly in resource budgets.
