I wouldn't call assisted suicide evil, and "purposefully killing their patients" is pretty much the description of a doctor whose job is to employ lethal injections.
What I find interesting is you describe a character as neutral who is doing actions you deem evil. To me, Neutral isn't just a transitory alignment between good and evil, requiring a balancing act of good and evil deeds to maintain. It's its own thing, so I would not make a statement that "Neutral characters commit evil acts". Neutral characters act in Neutral ways.