The most scary thing about this is not the legal ability to force companies to assist (I can easily get around that by creating my own crypto -- and non-corporate tools with no one to serve the TCN to will soon be widely available); it is the lack of visibility.
It should be essential that we, the voters, can track how much these powers are being used. Instead of being secret, every company should be required to announce when they receive a TCN, and the full details (including the list of who's communications were intercepted) should be published within one year (extended only on authorisation by a court, and only for individual affected accounts).
We know that powers such as these get misused (often with the best of intentions). Just look back at the history of cases of police infiltration of trade unions, campaign groups, human rights groups, anti-war or anti-bomb activists, etc. All with abuse of powers intended only to save lives.
I can understand the Australian opposition being weak and naive enough to be convinced that these (ultimately ineffective) powers are important. I can't understand them not requiring the removal of the secrecy as their price for approval.