Compulsory voting does no such thing. Australians begrudge voting (and that we must fully enumerate our preferences).
The pragmatic reason for having compulsory voting is to provide a better sample of what the population wants. In effect, to dilute the crazies.
Voluntary voting is dominated by the question of motivation and ability. Those who are motivated and easily able to vote set the agenda.
Ever wondered why US politics is dominated by so many basically tangential issues?
Because whether you are pro or contra, abortion / marijuana / the death penalty / public health etc are classic issues to Get Out The vote.
And the consequences continue.
Ever wondered why US politics is about soaring rhetoric and heart-crushing negativity?
Because the basic strategy is: inspire your own voters so they turn out ("Yes we can!", "America is at a crossroads") and make the other guy's voters disillusioned enough so that, while they won't vote for you, they'll just stay at home.
Australian politics is more about transactional than transcendental issues, simply because the great bulk of people are required to vote whether they want to or not.
To summarise: it does not greatly improve the quality of voters. It improves the quality of outcomes.
Yes. It forces the expression of weak preferences which otherwise wouldn't be expressed.
Transactional voting is perfectly adequate. Its the minimum requirement you need to have a successful democracy. It still leaves room for the politicians that want to inspire people, or try to make them fear the other candidate, etc. But it also makes people talk about the day to day business of getting by. We sorely are lacking that here in the US.
I don't care about improving the quality of voters implicitly. That is a side effect of mandatory voting. Improving the outcome is the primary target.
Overall, I appreciate your comments and take the view that they illustrate and expand on my points, rather than refute them.
Some examples in regards to one minority: