Just to preface this, I'm not arguing against the critique of the reactionary position in this meme, but speaking more generally and trying to round out understanding of the whole philosophical argument. We clearly know that the idealist free will position is inaccurate, but the mechanical determinist position doesn't give us the full picture either.

While our lives are shaped by our material conditions, we should always keep dialectical materialism in mind and not fall into a purely mechanical determinism that becomes a pessimistic or nihilistic fatalism.

From Gramsci:

We can observe how the determinist, fatalist mechanist element has been an immediate ideological “aroma” of Marxism, a form of religion and of stimulation (but like a drug necessitated and historically justified by the “subordinate” character of certain social strata).

When one does not have the initiative in the struggle and the struggle itself is ultimately identified with a series of defeats, mechanical determinism becomes a formidable power of moral resistance, of patient and obstinate perseverance. “I am defeated for the moment but the nature of things is on my side over a long period,” etc. Real will is disguised as an act of faith, a sure rationality of history, a primitive and empirical form of impassioned finalism which appears as a substitute for the predestination, providence, etc., of the confessional religions. We must insist on the fact that even in such a case there exists in reality a strong active will, a direct influence on the “nature of things,” but it is certainly in an implicit and veiled form, ashamed of itself, and so the consciousness of it is contradictory, lacks critical unity, etc. But when the “subordinate” becomes the leader and is responsible for the economic activity of the mass, mechanicalism appears at a certain moment as an imminent danger, there occurs a revision of the whole mode of thinking because there has taken place a change in the social mode of being.

We should always keep in mind that, despite the limitations imposed on us by material conditions and history, we are parts of the whole and not just passive entities being directed by outside forces. Our actions and choices, especially collective ones, do matter and are what shapes our societies.

As Marx puts it:

Men make their own history, but they do not make it as they please; they do not make it under self-selected circumstances, but under circumstances existing already, given and transmitted from the past.

Free will is a human's subjective experience making choices.

Determinism is describing that the more information about a system, the more the result can be predicted accurately. With perfect knowledge, one gets perfect predictions. (nobody will get perfect knowledge)

Both of these statements can be true without negating each others premise.

But why do people think there is some sort of contradiction?

Perhaps we should look at this dialecticaly.

A human body has desires and needs to sustain itself and also will do behavior to produce happy chemicals for the brain. The brain creates a model of reality based on its experiences in order to optimize the best experiences. People can calculate less optimal choices because of the incompleteness of their mental models of the universe. There will always be a contradiction between any brain's model of the universe and the actual universe. A mental model can be reinforced to make that mental model give feel good hormones to the body. When the universe demonstrates to the mental model that it is false in some manner it gives bad feeling hormones.

Most conservatives in KKKrackerland I have met seem to insist on free will because of the central point of their model is that the world that benefits them and they want to feel that they made the right choices. They tie their sense of self to their nation. When evidence presents itself that the nation is less than good they cling to the ambiguity to justify their "truth" about the goodness of the nation. Those that suffer are merely making choices that are wrong. If the impoverished and criminalized made the right choice, they wouldn't be poor or criminal. When they do criminal acts to hurt others, sometimes it is for the joy of hurting others. Other times it is because they know that they can get away with it and indifferent to the suffering of those they hurt.

Most liberals I have met cling to the model of determinism because they get pleasure from being correct more than identifying with victory. Some liberals of persecuted minority groups often identify with that failure and develop a sense of learned helplessness. If one does not believe in choice, one can not see themselves improving themselves or the world. When they do crimes its often because they lack the imagination to meet their needs in a legal manner.

As a communist I want to improve myself to give myself the power to help others, and in return, I need to have faith that those others will help me improve this wretched capitalist hellscape. I'm a highly empathetic person and I see the needs of all as my own needs. My research seems to indicate that socialism is the optimal means to stop others from harming me and harming themselves, for that reason I support socialism. I don't need to have 100 percent knowledge to choose socialism in a deterministic material world.