Admittedly I've only skimmed through the important parts of the study, but based on that, I think this seems like a really poor thing to pick out from the study - possibly even because this might not have been a focus of the study, but also because important context was left out (excerpt from the discussion section):
"It is possible that holding extreme (and thus unnegotiable) attitudes on important social-political issues has become increasingly identity defining for Democrats, not least in response to Donald Trump's controversial presidency. The pattern does not imply that Republicans are more tolerant than Democrats, nor that Republicans could deal better with attitudinal uncertainty. It does imply, however, that –at this particular moment in time– Democrats and Republicans are constructing and managing their partisan identities differently in relation to the topics reflected in these questionnaire items. Research suggests that social category membership (e.g., being White, Christian) is more important for the construction of Republican identity than it is for Democrat identity (Mason & Wronski, 2018). Fulfilling such normative criteria may hence qualify someone as a valid group member even if that same person may hold somewhat liberal views on, for example, gay marriage."
I feel like having this context from the start would have greatly benefitted discussion, which seems mostly of quite low quality to me at the moment. Research in general should, in my opinion, be cited and drawn conclusions from only very carefully, because it's incredibly easy to draw the wrong conclusions and focus on the wrong things if you're not an expert on the subject.
