Forcing anyone to do anything(outside of things needed to sustain life) hardly works without some major drawbacks. Someone who doesn't care about the political system won't care anymore when forced to vote. Also, scheduling such a task is very difficult in the US currently.
Voluntary voting means elections are won by political parties' organizational efforts to turn out their voters. Mandatory voting means elections are won by the parties presenting more appealing ideas to the voters. If you think elections should be more about ideas, mandatory voting is good for that.
Not voting is voting. Should someone come to the conclusion that the game is not worth playing, there is no reason to inhibit them from declaring this. The voter is expressing that there is no candidate which compels them to vote, a much stronger opinion than voting for the lesser of two evils.
This may lead to the view that voting is just another chore to be rushed through and not taken seriously. It may cause people to vote randomly or without due care, which could be catastrophic and ultimately further disengage the population from politics.
kjhealey
