I don't think this is fair at all. Communists don't need to tell the workers what their interests are - the workers already know that. I don't think you will find many workers who think being impoverished and starving is in their interest, unless they believe in some sort of heavenly gendarme who wants them to be impoverished and starving, which is simply a matter of having incorrect, unscientific beliefs. What bourgeois ideology does is, it convinces workers that there is no alternative. Class consciousness isn't about the workers recognising that, cor, all that starvation and easily-preventable disease really weren't in their class interest, but the struggling proletariat coming into awareness of the possibility of communism, and its historical role of destroying class society.
The rest of the post, I think, relies on a very peculiar notion of objectivity. Of course interest is not something that floats in the ether, but is formed by concrete human circumstances (and of course rocks don't have an interest) and interactions. The same goes for society in general. But neither is subjective in the sense that I can say society is whatever I please it is, and the same goes for interest. I don't think harm is really a completely physiological notion, by the way. There are things that mildly hurt us in a purely physiological sense, but that are not odious to us. It's not really cut-and-dry - what is, in life? - but I think most people can recognise the difference between an eclair or a light spanking and, say, killing yourself via autoerotic asphyxiation (which is not to say that the latter is "wrong", somehow, I don't think the recognition of interest implies any sort of moral malarkey; we talk about class interest, not because we think that people should follow their class interest but because as a matter of fact most people want to, even if they don't recognise it as a class interest).
Okay, there are at least two sets of problems here.
You claim that communists don't need to tell the workers what their interests are; and I agree. But the fact remains that social revolution and communist transformation have been argued for in terms of objective class interest. Communists have told workers' what their interest was, or at least about the only possible ways of realizing it. This amounts to claiming that irrespective of articulated points to the contrary, it is some kind of "interest" existing out there which the workers should realize, and its content is in short communism. The issue is not that banal so that we conclude it's not in the best of our interest to aim for impoverishment and so on; it's about the historical psychological-social formation of needs and wants and the ways of achieving them (also about what those ways entail, as I was aiming to show with the hypothetical example I provided).
This is the way communists (of course, not all of them) have dealt with problems in interacting with other workers, especially at socially and politically turbulent times. Another term which is very close is that of the historic mission of the proletariat, and I claim there's no such thing and that this is mere obfuscatory rhetoric.
So, the issue here is how communists relate to workers with whom their in significant disagreement. The idea of false consciousness is also raised here.
The second problem is what I think is your peculiar way of understanding how the word "subjective" can be used meaningfully. The sense you mention which supposedly enables one to say whatever the hell they want isn't the way it is normally used; we have another expression to cover that, it's called "bullshit". So the problem isn't subjective = idiosyncratic and fundamentally disconnected from the way things are. Not at all as the sensible way to talk about things includes judgement which isn't empirical, for example judgement of taste which is necessarily "subjective" as an expression of what one likes.
But if your argument would hold then we wouldn't in any way be able to meaningfully talk about subjective judgement and attitudes since the whole thing is illusory in the first place (or better yet, since the word denotes a process which is necessarily detached from our common world).
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“The possibility of securing for every member of society, by means of socialized production, an existence not only fully sufficient materially, and becoming day by day more full, but an existence guaranteeing to all the free development and exercise of their physical and mental faculties – this possibility is now for the first time here, but it is here.” Friedrich Engels
"The proletariat is its struggle; and its struggles have to this day not led it beyond class society, but deeper into it." Friends of the Classless Society
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