The idea of constitutional means to change the government is based on the existence of constitutional means to change the government.
This entails that those means must be available. If they are closed, the government is guilty of subverting constitutional means to change the government.
This happens when the government of the day compromises the electoral system through manipulation of electoral referees so that it’s virtually impossible to change the government.
This is what pushes people to use whatever means necessary as happened in Sudan recently.
Back in the 1960s and 70s, the black nationalists realised that conformity to the Smith system was never going to bring freedom.
Their only option was to break Smith’s law and do what was necessary to achieve freedom. Mnangagwa and company were part of that movement.
Smith and company called them terrorists. He imprisoned and tortured them. He was not ready to give up power so he defined them as terrorists.
Ordinary people called them freedom fighters. Because that’s what they were. Or at least the people believed they were.