this means that the starting point for each ideology is not experiential evidence, which is then used to construct an explanatory system, but rather a desired conclusion, generated by theoretical arguments
the conclusion here, being that all people are identical in their nature
this conclusion is desirable for the reason that it provides an excellent foundation for all sorts of rhetorical trickery; in the Soviet case, it was used to justify the state ideology, lending air cover to its failing policies (see Stalin famines)