All I can say is the mandatory voting that we have in Australia forcibly enfranchises the apathetic, a lot of whom will make their decisions as they stroll to the polling both or even as they're actually in the booth. Think about it. Do you really want the disinterested to vote?
I'm still somewhat undecided on the practice even if I don't mind the idea, but it's a moot point anyway, it'll never happen in the US. Given how partisan even the most basic election law changes are, there is no way there would ever be enough support for mandatory voting. If Democrats did try to do that, there would probably be a massive backlash. However, I still stand by this:
At the very least, we need to have same day/automatic voter registration, county-wide polling places, closing times at no earlier than 8, two weeks at least of early voting, permanent no-excuse absentee voting and a prohibition of photo ID laws unless proven necessary (there are better ways to prevent in-person fraud than photo IDs, which reduce young/minority turnout). There is no good reason we can't do those things, and the reason we haven't in so many areas is because of pure partisanship and the desire to win above everything else.
These are common sense changes that are pro-voter access but not reckless nor offensive to one's rights, and given how gracious Republicans have been to blanket the country with voting restrictions since Obama was elected, I'm hoping Democrats will ram through any/all of those changes the second it is possible, with or without GOP support.