at least have enough courage to admit that 4 teenagers would make you nervous. there's nothing wrong with being alert. teenagers can be dangerous and unpredictable. the dividing line IMO, would be behaving preemptively in such a scenario.

4 teenagers would not make me nervous. Happens many times per day for many of us. Parent comments are talking about something different than "common sense" or "being alert". Profiling is a real thing that many people have to deal with.