In Dante's Inferno, do the penalties seem harsh?No, that's all.
The penalties Dante creates for those who sin in Inferno can only be deemed harsh by an individual only. Some may believe that the penalties "fit the crime," others may believe that they are too lack, and others may believe that they are far too harsh. Essentially, the text is showing readers what Dante believed to be appropriate punishment for crimes committed and, therefore, cannot be argued (in terms of harshness) since they are offered as Dante's opinion (supported per the eNotes' "An Explanation of Dante's Hell").
Dante believed in the Roman idea of evil, so his structure of Hell is consistent.
That said, some of the penalties may seem a little backward. For example, the "magicians, diviners, fortune tellers, and panderers are all here" in the eighth level of Hell--The Malebolge, while those "who either wasted and lived greedily and insatiably, or who stockpiled their fortunes, hoarding everything and sharing nothing" are sent to the fourth level and the fifth level is designed for "the wrathful and the gloomy."
Essentially, given that Dante agreed with the Roman ideology of evil, the levels uphold the ideas which were widely accepted by those who preceded him, and it was not Dante, himself, who denoted the level of punishment.
All the penalties in Dante's Inferno seem incredibly harsh because of the fact that they are all destined to last throughout eternity. It is the time factor that makes them seem not only harsh but sadistic. Otherwise some of them might be called poetic justice. It is hard to believe that Dante was writing anything but poetry and that he was inventing torments that were metaphorically appropriate to the sins commited in life by those unfortunate souls he was observing. Eternity is endless. A billion billion years is only the beginning. Just being confined in Dante's catacombs without any kind of physical torture would be sufficiently excruciating if there was never any end in sight. Dante himself seems to have had a sadistic imagination--or else he should be taken as a grim comedian like the Emperor in Gilbert and Sullivan's The Mikado who sang gleefully about how he delighted in making the punishment fit the crime.