Batman has been characterized as more and more of an asshole for the past decades. Thomas Wayne was depicted as a flawed man but he wasn't a villain...
Superman has way more enemies in his rogues gallery that test his physical might than Diana does. Most of her enemies either don't have super powers...
It's not a matter of whether or not she should kill, it's when she should. Diana isn't a sadist or a murderer. She will kill when it is necessary and...