Are these powers an undue trespass on rights and liberties?

As stated in Laws of Australia vol 11 para 119:

At common law power does not exist for the personal search by police of suspects prior to their being arrested. There is no general power at common law ... enabling police to stop and search suspects, either by frisk or more intrusive search, or to seize their property.

This statement applies with more force to persons who are not suspects, such as those who might be able to assist the police in some way.

An unauthorised stopping, detention, or search of a person would constitute one or more forms of tortious or criminal behaviour. To stop a person and restrict their movement may amount to a false imprisonment. A search of a person involving any physical touching would involve a trespass to the person. A taking hold of their possessions, including a search of their baggage, would involve a trespass to property.

It is sensible to speak of a "common law principle of bodily inviolability", as did the majority of the High Court in Marion's Case (1992) ... Their Honours approved of a view that this principle was allied with, or the basis for, a right to privacy. In relation to powers of search, detention and the like, the common law began from notions of right to property, and to bodily inviolability. There is a link between the latter and the notion of a right to privacy, and it is this right which is nowadays seen as the starting point for an assessment of the desirability of these kinds of powers. For example, Feldman states that "[s]top and search powers have been described as 'a major interference with people's right to privacy, and a relatively minor interference with the right to freedom from physical interference'": Feldman, Civil Liberties and Human Rights in England and Wales.