Communism is indissociable from its three components, which includes a political system: dialectical materialism (the philosophical part), the labour theory of value (the economic part), and the class struggle (the social thus political part).

Anything other than Marxism is ineffectual in the real world and leads to nothing as exemplified by 200 years of history. "Tankies" don't "happen" to have an economic theory, it's an integral part to the whole of Marxism and Marxism could not exist without the economic basis for it. Why do we dislike capitalism? Because through math we can prove it is rife with contradictions and invariably leads to imperialism. Otherwise why would we want communism? Just because it's cool to be a communist? Just because it's a hobby? There has to be an actual justification for what we want.