What would Robespierre and Burke have to say to each other, if they somehow met? How would they justify their opinions to each other, for example? Are revolutions justified? Is what revolutionary leaders sometimes do justified?

A conversation between Maximilien Robespierre, the radical architect of the Reign of Terror during the French Revolution, and Edmund Burke, the father of modern conservative thought and a fervent critic of the French Revolution and the revolutionary impulse, might be quite bizarre. The two figures stand on totally opposite ends of the political spectrum and would likely have a hard time discussing politics civilly with one another.
For Robespierre almost any act was justified in the interests of supporting the spirit of the revolution. As the leader of the Committee for Public Safety, he carried out murderous acts in defense of the revolution.
In contrast, Burke was a conservative—the original conservative. An Irish-born statesman and British MP, he wrote a series of critiques of the revolution that eventually became a book, Reflections on the Revolution in France. His view was that radical revolutionary change was contrary to the "natural" order of things. He defended the idea of class and privilege and even supported the suitability of the aristocracy to rule.
Burke would be deeply critical of Robespierre's revolutionary actions and his justifications for revolutionary violence. Robespierre would have no patience for Burke's whiggish conservatism and probably try to figure out a way to have him killed.