Norman Bates does not usually spring to mind when listing 'bad guys'. He's somewhat 'soft' in that department. Sure he killed women, but he was wearing a dress!
More seriously: being bad or evil is magnified by it being a choice on the part of the character. One chooses to be one or the other; it's the volitional commitment to/pursuit of evil ways in the face of the possibility of
not being 'bad' that makes a bad guy truly bad. Norman Bates was driven long ago to where he was no longer able to make any choice: he was unable to respond in any other way. That lack of choice - being so damaged as to be unable to choose - makes the character pathetic and we can end up sorry for him rather than afraid of or hating him. He cannot be blamed for what he does.
