You also have to remember that comics were seen as kid books back then too. I doubt any parent knew their 1st grader was reading a book with a murder being committed. Comics were .20 then and available everywhere, and the general public equated them with shallow cartoon stories. So a generation of very young readers got a huge shock when they were not
expecting it. As I'm sure you have heard, nobody of this stature had been killed off before, so there wasn't a reason to expect it. Today, it would be old news by the time it was released.