They design their studies based on the assumption that egalitarianism is true. The study will produce inconsistent results, exactly like dividing by zero or assuming circles have corners.
Fascism is egalitarian fundamentalism, and all psychologists are Fascist.
Their studies will only replicate by accident. When they mistakenly scuttle their own assumption. E.g. if they control for something that effectively means controlling for class, and thus compare the middle class to itself.