He has the power to wipe out the entire human race and if we believe there is even a one percent chance that he is our enemy, we have to take it as an absolute certainty.
Batman can do math. On the Justice League, he is called, “The Smart One.” He is a detective. He would detect who is guilty, who is innocent, and who does and does not need a Bat-punch in the mush. Read The Dark Knight Returns, there are better ways to give me a Bats-vs-Supes smackdown (and a serious fanboy orgasm!) than that one-percenter line. It is lazy writing, and it sucks. Even an NPR critic did a double-take at that.
That line reminds me of an old joke from Steve Landesberg (Dietrich from Barney Miller). Steve was doing the character of a Deep South sheriff. His accent was perfect. (The quote below is from my memory, so is not likely exact. Except for the punchline.)
“Yep, ah’ve been at this job a long time, I can tell just by lookin’ at someone if they’re gonna do a crime. Just yesterday, I saw a guy, and just by lookin’ at him, I know he wuz gonna kill someone.”
(Perfectly timed comedic pause.)
“So I shot him.” (Audience laughter.) “He ain’t gonna kill nobody now!”
Batman is smarter than that sheriff. DC Comics, when you make your next movie, please hire a writer.