Based on the sources available to her mid 19th century, I can totally see how she got to that conclusion (which btw is elegantly phrased), but I have to say, Frédéric ne connaissait ni l'envie ni la haine cracks me up. I mean, this is totally the image he worked for! (And also, she's absolutely right these "little passions" were very much part of Voltaire. More about V in the other comment.) But good lord, did Frederick ever know envy/jealousy and hate. Leaving aside all the complicated family relationships where this is demonstrated a plenty and sticking solely to a Voltairian context, he was ragingly jealous of Émilie du Chatelet for as long as she was alive, having identified her as his main competition for Voltaire, and could be incredibly petty about her because of that. Though decades later, after Voltaire's death, also repentant: Frederick's obituary speech about Voltaire contains a lovely Émilie passage, acknowledging her as a scientist and what she had meant to Voltaire as a person in a way his younger self had not been able to.)