Whenever foreigners discuss Australian politics, they always have a freak out about mandatory voting. And I find that rather odd.
If a government is going to claim to represent the "will of the people", it needs to be ALL the people. Not just some. There is a whole group of people that are not interested in your bullshit. And if their vote isn't counted, then the loudest group of bullshitters wins.
At least that's the steelman position. IMO the organised minority wins anyway no matter what.