Acharya Prashant explains that nationalism founded on common language, religion, or ethnicity is inherently dangerous and divisive. He argues that most forms of nationalism arise from the ego, which thrives on boundaries and separation. When a nation defines itself by its differences from others, it inevitably leads to hostility, conflict, and violence. He cites historical examples like the two-nation theory and the division of nations based on language to illustrate how differences are endless and lead to discord if made the foundation of a state.