"If there is even a one percent chance he isn't on our side, we have to take it as an absolute certainty!"*
-
Now, I realize that Batman is just paranoid enough to devise schemes to neutralize any and all members of the Justice League, just in case they go rogue or are mind controlled (which is far more prevalent in the comics than in the movies), but that kind of blustering rhetoric, and looking for a fight just because, isn't Batman.
Whatever.
All hero versus hero plots need some form of macguffin to put them at odds with each other. It's not like Snyder was faithful to the psychology of Superman in MOS, either...
*Seriously, who wrote this script? A twelve year old? Michael Bay? I mean:
"Hey, if this dude is like only 99% friendly, he's totally a bad guy, bro... we gotta take him down..."