I think The Reign of Terror was a necessary reaction to the politics of the time. The purpose of the reign of Terror was to purge France of the enemies of Revolution and protect the country from foreign invaders.
There is no denying that the Reign of Terror was dreadful. In the course of nine months, over 16,000 people had been guillotined. This was necessary to take out “the internal enemies of France”.
At a point, the reign of terror was no longer necessary but Robespierre continued the terror because he wanted to purge France completely of everyone who was corrupt. The Reign of Terror ended when Robespierre and his allies were executed and the armies of France were successful against their enemies.