Dialectical Materialism and Socialism

Marx derives Dialectical Materialism as follows.  First, according to Hegel, Mental processes necessarily tend towards Totalization, via a synthesis of opposites.  Second, Mind is Material.  Therefore, the internal dynamic of Matter is Dialectical.  So, applied to Society, the elimination of Classes is inevitable, with Socialism the result.  Now, the main weakness in the derivation is the dogmatic reduction of Mind to Matter, not only because the thesis is only one of several familiar varieties of their relation, but also because it accepts the traditional concepts of each.  Furthermore, evidence of Dialectical Materialism is lacking, e. g. the concept of sexual activity as a 'synthesis of opposites' is inadequate, since in combination with the resultant, the sequence better evinces a pattern of Diversification, rather than one of Totalization.  So, the imposition of Dialectical Materialism on History is not only questionable, but obscures the most compelling argument for Socialism--that it corrects the injustice in Capitalism that profit is stealing.