i touched on this issue a couple of days back... apparently plenty of people are thinking and writing about it: cyron.id.au | Don't vote, you'll only encourage them!
it's hard to ignore the points raised in the article: why would you want poorly informed, unmotivated people to vote at all? a large proportion of the populace don't know the first thing about who or what they are voting for. they don't make any attempt to think; or even just keep track of which pre-election promises actually come true.
one reason to make these people vote is... if you make all of these people vote, then their poorly informed vote is just one of however many. even if they are spurred into voting one way or another by a weak argument, it doesn't mean that a relatively small number of idiots can force the outcome.
it's pretty damn harsh to actively dilute the worth of a single vote; but think of it this way: would you rather give a knee-jerk idiot/bigot/etc voter a proportionately higher say in an election? or would you rather limit the power of lobby groups to mobilize a mindless army of idiot voters? ...well, ok. i'd rather have a group of intelligent, informed voters. but that doesn't seem likely.
as for the point that refusing to vote would send a message to the pollies... well, if you are not a potential vote; as if they would care about your opinion! personally i think it would be better to have a kind of formal-informal vote. as in, the ability to formally refuse to vote for any candidate. sure, we can enter an invalid vote; but that is counted together with votes which were actually screwed up. to put it another way: an informed, purposeful, protest-based "informal" vote is counted the same way as a vote by someone too stupid to even fill in the form correctly.
i can imagine plenty of electorates could record a very high level of protest vote. that might shake things up a bit... if you couldn't get a result without 50%+ of the voters actually casting a supporting vote, they might work a bit harder. plus i think it would appeal to australians to be able to tell the parties to go find someone worth voting for :) even being able to specify that none of your preferences should go to another candidate would help. i know voting is mostly about who you put last (as observed by Andrew Denton)... but when you only have two options that is also the person you put second.
democracy: it's not great, it just sucks a bit less than other systems.