>that one's position/class/socio-economic-factors are the determining factors in their values and beliefs.
Have you actually read Marx? Nowhere does he make this claim, nor inspire this thought. I don't know where you're getting this from. Marx does not deny the indidual's individuality. Here's a little quote, which is a criticism from Marx of the very view you are accusing him of:
>The materialist doctrine that men are products of circumstances and upbringing, and that, therefore, changed men are products of changed circumstances and changed upbringing, forgets that it is men who change circumstances and that the educator must himself be educated. Hence this doctrine is bound to divide society into two parts, one of which is superior to society. The coincidence of the changing of circumstances and of human activity or self-change [Selbstveränderung] can be conceived and rationally understood only as revolutionary practice.
(From Theses on Feuerbach)
Please don't accuse us Marxists of the fallacies you can't back up. Besides, even if Marx was accused of economic determinism, it doesn't mean that the critics are right. In fact, here's yet another statement from one of the founders of Marxism (Marx's close friend Friedrich Engels):
"Marx and I are ourselves partly to blame for the fact that the younger people sometimes lay more stress on the economic side than is due to it. We had to emphasise the main principle vis-à-vis our adversaries, who denied it, and we had not always the time, the place or the opportunity to give their due to the other elements involved in the interaction. But when it came to presenting a section of history, that is, to making a practical application, it was a different matter and there no error was permissible."