Compulsory voting is a needless encroachment on people's freedom to do as they please. People can't be bribed to vote when they're required to vote? :)

It may seem weird, but there are families so destitute that they may have better things to do than vote.

The voter turnout will be just fine without compulsory voting: http://en.wikipedia.org/wiki/Voter_turnout#International_dif....

Looking at the comments again, tjogin summed it up pretty well.