Or more to the point: how many checks exist (if any) between such a 'tip' identifying someone as a possible threat, and their being identified as a 'terrorist' by the executive branch and essentially stripped of their rights as a citizen?

This is why people don't trust the administration's argument of: "we'll only use it on real terrorists, we promise". Not only is that still a terrible affront to liberty, but our country's track record of identifying "real" terrorists has been laughable. The very concept of any practical "trust" in their ability to operate in this space is made laughable by situations like the deportations in question.