I agree with the first part of the sentence, but not the second. If what you suggest is ok, why then did the police dispatcher specifically say to Z that "we don't need you to do that"?

Why is every organized neighborhood watch group in my area specifically instructed to observe and report suspicious activity, but never to follow and confront?

Someone either earlier in this thread or, possibly at another website, raised the issue that "following" a person under certain circumstances may constitute the criminal act of "menacing" in some jurisdictions.