You're absolutely right that in a government context, consent is not always required for a government to collect information. The situation doesn't arise in quite the same way. We have rules already in the Privacy Act for this.
One rule is that, as it stands, government should collect information, to the extent possible, directly from the person interested in the information, either with or without consent, say, in a law enforcement situation. The principle is to collect directly from the individual, which then leads to questions around what's on social media or potentially publicly available. That's a difficult area to navigate under the current act. But the first principle is to collect normally from the individual concerned, with or without consent. That's not the quite the same situation as for the private sector. I agree that consent is not always required.