We need to remember that the code of beliefs that Dante adhered to was rather different to what we might believe in today, and the time that separates our world from Dante's world has caused many changes in the way that we view subjects such as sin and punishment. Basically, this entire text is one that states a belief in a supreme God of justice. However, at the same time, Dante also believed in free will for humans, and therefore he saw that in a sense, there were no "innocent" characters in hell, only characters who had not made the right choices during their lives.
Again and again, Dante shows that although the characters inhabiting hell may not have been "evil" as we might think of the word, they set their own wills against God and his plan for them during their lifetime. All the characters are therefore in hell because of their failure to make the right moral choices. However, although this sounds very harsh to our modern ears, at the same time, we need to remember that Dante equally stresses that had they confessed and repented of their misdemeanours whilst alive, they would have experienced God's redemption and gone to heaven. Therefore, what unites all the characters who dwell in Dante's hell is that they have all, no matter how much or how badly they have sinned, defied God and lived their lives the way that they want to.
I understand the difference in time periods and codes of belief, however, I'm wondering about the separation that Dante creates between these particular characters (and possibly others) and the shades that he condemns for their sins. These characters are separated and pitied by Dante the character, and I was trying to pose a question as to why they are singled out in hell as more "innocent" characters?