As Allen in Oz has pointed out - voting is not compulsory in Australia. Turning up at a polling station and having your name marked off is compulsory. How you mark your ballot card is up to yourself. Some people just write "Get Stuffed" across it. The percentage of this "Donkey Vote" is quite small.
My opinion is that there are more positives than not in compulsory voting attendance.
I cite the example of our waterside worker unions ( longshoremen ) in the late 40's & 50's. The election of union officials was not a compulsory vote. The apathetic unionists didn't even bother to go to meetings. The dedicated communists did. Before they knew it just about all our waterfronts were subject to communist controlled unions. The industrial unrest this caused was most significant.
Now, if compulsory voting attendance wasn't in place, it would be possible for a minority fringe group to end up running the country.

JG/FME