This isn’t inherently true. Nationalism in the context of liberation from colonialism and imperialism is an inherently progressive project, as it creates national autonomy. Nationalism in Israel’s case protects its status as a settler-colony and is inherently genocidal and reactionary.

Further, major resistance groups in Palestine like the Popular Front for the Liberation of Palestine are Marxist-Leninist, which is inherently left-wing. Hamas is not the only group in the resistance, just the primary.