In democracy, the majority rule. In liberalism, freedoms are protected. The first one doesn't necessarily mean the second one (see 1930s Germany). And the second one is hard to interpret without the first one. That's why we're 'liberal-democracies': we like to be both.
Australians want to inflict pain on asylum seekers who arrive by boat. Election after election, poll after poll, we know a majority of people want this. So as a democrat, you can't deny them that. As a liberal, you can.
As a liberal, you can say that the freedom of Australians to not want people arriving by boat because they have irrational fears is a lesser freedom. It is a lesser freedom than the freedom of people, including children, to not have indefinite detention for no crime.
But perhaps a majority of people would see the first liberty as more important than the second?
Unfortunately, we have no bill of rights to sort this out. And even the U.S. doesn't have a bill of rights that extends to foreigners. As for the international order, while the UN can chastise, it can't rule.
A majority of Australians want to deeply hurt a small group of people: what can you do?