What belief is exhibited by someone who thinks only a specific political party's ideas are valid?

The belief exhibited by someone who thinks only a specific political party's ideas are valid is described as partisan bias. This concept refers to the tendency to favor one political party's views, policies, and beliefs while dismissing or devaluing those of others. A person demonstrating partisan bias might analyze information and arguments primarily through the lens of their preferred political party, leading to a skewed understanding of political discourse and decision-making. This phenomenon often results in an inability to critically engage with or appreciate alternative viewpoints, as there’s a strong inclination to believe that the party one identifies with possesses the only legitimate or truthful perspective.

In contrast, intellectual rigidity can apply to various contexts, not just political affiliations, and refers to a broader inflexibility in thinking. Conservatism is a specific political ideology that may or may not imply a disregard for other viewpoints, while rationalism emphasizes reasoning and evidence-based argumentation, which ideally involves considering multiple perspectives. These distinctions clarify why partisan bias is the most fitting term for the belief being described.