In case it wasn't clear, the GP was alluding to Hitler. I was noting that Hitler wrote Mein Kompf while in Landsberg jail on charges of high treason as a result

In case it wasn't clear, the GP was alluding to Hitler. I was noting that Hitler wrote Mein Kompf while in Landsberg jail on charges of high treason as a result of the Beer Hall Putsch. So he isn't really the exception the GP was musing he might be (being in jail provided the same benefits in terms of disposable time as being an aristocrat).