What happens is that many people who don’t really care about politics most of the time take notice in the last few weeks of an election campaign because they know they will be voting. While not perfect, I think the good of “compulsory voting” outweighs the negative.
It's led to some claims that our democracy is becoming dysfunctional and growing calls for PR or electoral reform.
At least with compulsion you have to be positive in your apathy!
We have had the fine system since the 1920s so it is really hard to know how it affects the political process. One thing it does do is get the turn out to >95% (we also get a fine if we don’t register too).
One of the big positives is it takes away the decision of voting or not - it is just one of those things like paying your taxes that you have to do.
Preferential voting means it's harder to shift the mean anyway, because parties have to appeal to other parties/interest groups to get preference deals etc (of course no one has to follow a preference voting card!).
Secondly, having 98% polling day turnout means you don't have to build outrage to get people to vote (as they do in the us/uk). I remember hearing that if polling day was rainy in the UK the conservatives could usually count on a 10% boost because their constituency have cars and the working class don't - not sure how true this is these days
The good thing is it is mostly just noise - what actually gets through the parliament is much more benign.
http://www.itv.com/news/wales/update/2015-05-08/angry-voter-...