I need to start collecting a list to turn this into a proper Thing but I feel like whenever there's a way to use technology for evil there's a Tel Aviv startup that cranks it to 11.
I get your point that a system that claims to detect terrorists but only really detected Arabic people would be an evil one - but you're automatically calling the terrorist system evil without knowing if it really does detect terrorists or not.
As an extra hypothetical question, do you feel a system that could detect people who were really just about to commit terrorist attacks as good or evil? At a conceptual level, assume the system somehow scanned brain waves or some other truly difficult method.
I don't care about that hypothetical. Save it for your sci fi screenplay.