Are you referring to the final suggestion? If so, I think it should possible to analyze the data to avoid this. There are (very roughly) two ways to get low covariance between opinions: one is to have low variance in opinions generally (i.e. to have middling opinions on everything) , and seems to correspond to centrism. The other is to have a low correlation between opinions (e.g. you could have more extreme opinions, but from both ends of the political spectrum). If you focus on covariance, you’ll capture both, but because correlation is normalized for variance, focusing on that should help avoid “centrism bias” (I think).
Are you referring to the final suggestion? If so, I think it should possible to analyze the data to avoid this. There are (very roughly) two ways to get low covariance between opinions: one is to have low variance in opinions generally (i.e. to have middling opinions on everything) , and seems to correspond to centrism. The other is to have a low correlation between opinions (e.g. you could have more extreme opinions, but from both ends of the political spectrum). If you focus on covariance, you’ll capture both, but because correlation is normalized for variance, focusing on that should help avoid “centrism bias” (I think).