The right to silence is one of the most basic rights a person has under the various justice systems that operate in Australia. The central premise is that the state is not allowed to force someone to incriminate themselves, because frankly, that sort of thing tends to lead to false confessions and the jailing of innocent people.
Unfortunately, this right is not something ensured by the constitution. Instead it's what's known as a common law right, something backed by precedent and case law, but vulnerable to legislative change. In NSW last week we saw exactly that.