The original work by Cesare Beccaria has a "commentary" attached by Voltaire. We must use quotes for "commentary", since this is really a separate rant against Christianity, along with a senseless romanticizing of everything non-Christian, especially the former Roman Republic and Empire. As such, it hardly touches on Cesare's work. Voltaire begins with an example of a young lady who abandons an illegitimate baby, and is then executed. The story is a tear jerker, but should remind us that we really haven't solved this problem today, except to introduce a multi-billion dollar per year industry to abort all the unwanted pregnancies. And we still have plenty of children abandoned, abused, and sometimes killed by their parents.
There is a section on witches that deserves a little comment. Voltaire's argument is that condemnation of witches was the result of ignorance regarding their powers, which is a popular misunderstanding today. Plato in his Law's originally condemned witches to death not so much for their supposed powers, but due to the terror they could cause in someone. The Romans too frowned upon the bloody human sacrifices of the Druids, so it seems to me that the entire argument got skewed somewhere along the way.
Much of the rant is against the severe and inconsistent laws of France which stand in contrast to those of the Roman Code of Justinian. What is not mentioned here is that France was taken over by a variety of tribes that were quite severe, including the Saxons who liked to exterminate the peoples of the new lands that they wanted to settle. I don't know why we expect the French to act as if they were descended from the Romans. Didn't Voltaire read Asterix???
Then there is a long itemization of crimes done by those seeking power or hoping to exterminate potential rivals. I suppose this is a universal property of power, that the worst of society will do whatever it takes to grab and cling onto power, even if that power is simply the leadership of a Christian parish. Often the laws are corrupted by one person who simply wants to justify a particular excess. So the history of Europe's attempt to extricate itself from the power of a Catholic Church gone mad along with all the resulting bloodshed makes for gruesome reading. But then there was the French Revolution. And the Paris Commune. The real issue is the sin nature of man and how to tame it.