It was a nice way to think of course and Lily wouldn’t deny that it is entirely likely. But the type he had been looking into? The magic? How could that not be viewed as the magic and not the wizard. Some aspects of dark magic may logically come of use but not a lot of it. The cruciatus curse for example. That certainly could be used as proof of those who have less than kind ideas using already at hand dark magic. Because it really is. And she knew how it can corrupt. She really did not want that for her grandson.
“It may be the case, at times, that a wizard chooses to use magic for evil purposes but that is not always true. Magic can, and has, corrupt many. Even those who are so pure that it cannot be believed. Those like you.”