They simply take it for granted, assuming that it is the right and only way to view the world

Some of the new research which is beginning to emerge about the nature of bias, not as a trope hurled instinctually by the progressive against the norms but as a symptom of thinking which afflicts everyone.

From “Equalitarianism” and Progressive Bias by Bo Winegard.

However, other researchers have expressed concern that this unflattering image of conservatives might be an unfortunate manifestation of bias from within the academy. Because most social psychologists are progressives, they simply take progressivism for granted, assuming that it is the right way to view the world and that, therefore, any divergence from its tenets is wrong and requires explanation. This leads to disparaging depictions of conservatives in the same way that having evangelical Christians study doubters would lead to disparaging depictions of atheists (imagine the scales: Unholy Skepticism Scale, Doubting Thomas Scale, et cetera). Scholars have begun to support this argument with research that suggests that progressives and conservatives are equally biased so long as scholars examine the right topics and targets. In fact, in an upcoming meta-analysis (a study that combines all effects from other studies), Dr. Peter Ditto and his colleagues found no statistically significant difference between progressives and conservatives on measures of bias.

There is reason to believe that Dr. Ditto et al.’s meta-analysis actually underestimates progressive bias (and possibly overestimates conservative bias) because it contained only a few studies that were directly about one of the most potent sources of progressive bias: perceived victims’ groups (e.g., blacks, Hispanics, Muslims, women). My colleagues and I recently wrote a manuscript that supports this speculation with a few studies, and we are conducting more as I write.