My take on compulsary voting is this.

A democracy only operates properly if the people do their duty and vote.

We all have rights in a democracy and hand in hand with rights goes responsibilities. You have no say in paying taxes you have to and voting is in the same category. So you vote or get fined.

It does get a much more representative result. Not too many people vote informally. Often the ones that vote informally do so because of their misunderstanding of how to vote not through submitting a blank voting slip.