Was the Reign of Terror in France justified?

The Reign of Terror came out of a period of great political turmoil and conflict. The crowned heads of Europe had waged war on revolutionary France, and there was a growing sense of patriotism among the French people who felt they needed to defend "their" revolution against the imminent threat of foreign invasion.
When people decide to take on a foreign enemy, they invariably also look for enemies within. As well as fighting against the armies of Austria and Prussia, the revolutionaries were also engaged in a bloody, bitter conflict with domestic counterrevolutionaries who wanted to restore the ancien regime. The army was on the verge of defeat, and the revolutionaries were utterly convinced that the deposed monarch and his followers were conspiring with foreign powers to destroy the Revolution once and for all. The very existence of the newly-forged nation was at stake.
It is little wonder then that in an environment of suspicion and paranoia, those in power wished to impose a Reign of Terror to crush their enemies. Desperate times called for desperate measures.
At the same time, however, there was undoubtedly an ideological edge to the use of terror as a revolutionary tactic. Leading revolutionaries such as Robespierre openly justified the use of terror not just on practical grounds, but also on moral grounds. Robespierre was obsessed with the idea that the purity of the Revolution was under constant threat, both from internal and external opponents. Virtue was the governing idea in peacetime, but it needed to be linked to the implacable use of terror in times of conflict. Robespierre regarded himself as the most virtuous of revolutionaries, so he naturally saw it as his duty to spearhead the campaign of terror which he and the other Jacobins unleashed upon France.
The Reign of Terror, forged in the heat of war, was ultimately undone by it. As the French Revolutionary Army notched victory after victory against foreign counter-revolutionary forces, it became harder to justify mass repression. Yet, if anything, Robespierre intensified the terror even more. In the process, he alienated many of his former comrades, who feared that they would be next for the guillotine. The radical revolutionaries had overplayed their hand and their fate was sealed. 
Whatever the justification, there can be no doubt of the immense suffering caused by the Reign of Terror. Tens of thousands perished. The overwhelming majority of people killed were not, as legend would have it, aristocrats or conspiring traitors, but ordinary men and women often sent to their deaths on the flimsiest of evidence.
https://www.historytoday.com/archive/robespierre-and-terror