TO THE MARXIST THEORY OF TRUTH
As we may notice from the above-cited words, Marx — who, in broad terms, is neither a modernist nor a postmodernist but a dialectical materialist — DOES have an objective understanding of human nature, though, as he himself recognises, human nature is "shaped", modified, by the dynamics of a mode of production. What I personally argue is that an objective conception of human nature may be based on the objective categories of individual needs that all human beings share, irrespective of religions, beliefs, gender, systemic hindrances etc.
This epistemological approach based on "human needs" appears quite neglected by the Postmodern advocate of "multi-truths". In fact, there is only one method, one "truth", through which human and systemic contradictions — and with them all the anti-human consequences — are abolished; that is to say, Marxist thought and praxis.
The "multi-philosophical" post-modern approach starts faltering whenever we raise the question of "needs realisation". What I argue is that a moral theory of truth can be only a materialist one that sees the individual drive towards the realisation of his/her needs, first of all, as true, as observable and then sees the aim of realising people's needs as a moral necessity, insofar as the human beings are by nature all (true) social beings, not isolated self-sustaining animals. Hence a moral theory of truth that is not genuine, that is to say, a moral theory of truth that doesn't take into consideration the genuine personal drive towards the maximum qualitative and quantitative realisation of one's needs (all, including the social ones), is not a genuine materialist one, but an idealist one. Hence it is a false theory of moral truth.
Communism, with his lack of contradictions, aims at providing the economic and political bases for the achievement of the realisation of natural human needs, the entirety of people's needs, through the provision of socially necessary use-values, and therefore at implicitly validating a pro-genuineness theory of truth.
They see the ruling mode of production — namely, Capitalism — as something eternal, value-free, something dropped from the sky as a 'gift' and as 'the best of all possible worlds', not as an historical and transitory produce; like the plant Engels was talking about in his scientific example on the Dialectics of Nature; the very same plant which would give rise to an entity whose resemblance would be that of an “improved” original form.
In fact, the common Bourgeois is afraid of Communism because he rightly fears his methods of economic immoral appropriation — namely rent, interest and/or profit — are going to end soon with the abolition of Capital and Wage-Labour; and therefore the rise of Communism.
In doing so, s/he fears his (bourgeois) individuality is going to end since exploitation — according to this historically “modified” queer individual —is not an anti-human element but an element composing his true 'individuality'. As Marx suggests, such a Bourgeois would regard himself as an individual, only insofar as he's a Bourgeois. Such an individual would not regard himself as a social being.
His words on the effect of the introduction of machinery on the employment of workers are a clear testimony of this insightful, though limited, “consciousness”.
The great merit of Ricardo, according to Marx, has been of perceiving the connection between the quantitative worth of commodities (their exchange value) and the total labour-time necessary for their production.
For Ricardo, profit is regarded as a uniform rate, which is proportional to the size of the capital advanced (and is still considered as a 'legitimate' deduction from the commodity’s monetary realisation). However, how can Ricardo attempt to analyse the effects of a uniform rate of profit on prices, asks Marx, when nowhere he attempts to define what determines the level of this (uniform, according to Ricardo) rate of profit? 
Leaving aside an analysis of his inconsistencies for the sake of clarity, it is important to point out that modern bourgeois economics hasn’t even reached the witty conclusions of Mr Ricardo. Modern economics can’t even see ‘antithetical interests’ in Capitalism. By not grasping the relevance of the concept of opposite/contradiction, as intended by Engels’ concept of Dialectics — it even ends up neglecting its own dynamics.