Voltaire never said or wrote that. 

https://www.themarysue.com/voltaire-beatrice-evelyn-hall/

"I will defend to the death your right to be properly cited."

In reality French Revolutionaries spent as much time sending each other to the Guillotin, as they did beheading Aristocrats and suspected "counter revolutionaries"

http://www.historywiz.com/terror.htm

https://www.britannica.com/event/Reign-of-Terror

The claim that Joseph-Ignace Guillotin was executed on the Guillotin is an example of Trump style history. The actual victim was J.M.V. Guillotin, a doctor of Lyons.

https://en.wikipedia.org/wiki/Joseph-Ignace_Guillotin#Family