During World War II, Germany had banned connection to non-local radio transmissions in order to immerse the population in Nazi propaganda. The argument Werner and Jutta have is based on morality and ethics. Jutta listens to broadcasts from other countries, which speak of Germany committing "atrocities".
Jutta believes none of the Nazi's propaganda and seeks to find out the truth about Germany's actions. She asks her brother if it is right to conform to Germany's nationalism just because others do. Werner had been given an opportunity to escape the coal mines and attend a school for Nazi teenagers after impressing Rudolf Siedler by fixing the man's radio. Werner destroys the radio, choosing to conform and effectively alienating his sister. Jutta interprets this action as Werner's betrayal of his morals and identity.