I would assert that giving Aboriginal peoples a voice in government is a "bare minimum decency" sort of thing, rather than some sort of abstract attack on "basic principles of liberal universalism".
How do you personally choose whether an indigenous group have a right to be represented? For example, should people in Britain who can trace their ancestors to the Mesolithic gain this right too?
Perhaps a referendum would be a good way to do it? The UK has proposed, and even passed, a few of those in recent memory
Please, stop the train, I want to step down...
Are the people of the UK feeling represented since all those referendum passed?