There has been a global trend for decades among free nations with representative government, a decline in voter turnout in elections. In 31 nations, spread over every continent, the franchise - the right to vote - is treated as BOTH a right AND a civic duty. Right and duty are treated as two sides of the same coin, as well they should be, and as our own founding fathers (and mothers) strongly believed. The argument is reasoned that the greater the participation of the electorate, the more legitimate the resulting representative government - in the U.S., a hybrid democratic/republic in form.
Like serving jury duty, like paying taxes, like obeying laws, like males registering for the selective service at age 18, and now in many instances purchasing health insurance, performing one's civic duty comes with modest appropriate penalties for failure to perform as required. In no instances of failure to comply with compulsory voting has anyone been incarcerated; the range of penalties are highly varied from one nation to another.
Belgium was the first country to try this, back in the 1890's; it is far from an unproven experiment in practical civics. Other countries, like Australia, did this back in the 1920's, coming up on 100 years ago. It's been under discussion in the UK for a few years now, we would not be unique in considering this change. So far as I can find, there are no provisions of the U.S. Constitution, or my own state equivalent, that preclude this. I don't claim to have read every state constitution of the nation's 50 states, but in the course of research on various topics, I've probably read about a quarter of them, so based on the similarities between them I would be surprised to see that any state precludes this. The concept should not present a serious constitutional obstacle.from the Skillet Creek Journal, Baraboo, WI
In addition to addressing a drop in voter participation with a proven solution that has worked in a variety of countries, we have the additional battleground of attempts at voter suppression in the enactment of laws that deny legal voters their right and reasonable opportunity to vote, as we have seen in a variety of states. If we have compulsory voting, states will be pushed to provide adequate polling opportunities, instead of those shameful locations where people waited in lines for hours, or had to come back multiple times to cast a ballot. While it is true that some people, immaturely, would cast blank ballots, in practice, this has not been a problem. Most people, once persuaded to go vote appear to do so with some degree of sincerity in their participation.
Personally, for those who insist that NOT voting sends a message, I would argue that the message is not so much disapproval, as it is that people have gotten lazy and apathetic. But to accommodate those who wish to express their disapproval, I think we should begin to include on all ballots the option to withhold one's vote, or vote 'none of the above' in any race which also permits write-ins. To be affirmatively elected, a candidate running unopposed would have to receive more votes than 'none of the above'. I think voters grudgingly dragging themselves to the polls might appreciate the opportunity to vote against a bad slate of candidates.
In the U.S., we average around 51% voter turnout in general elections (not just presidential elections, but averaging off-year elections as well); in my home state, we've had the highest turnout in 8 of the last 12 elections, around 75%. In other nations, especially those with compulsory voter participation in elections, the typical vote is in the 80% to 90+%. Our turnout rate to the polls is remarkably poor, and getting worse, for the most part, not better.
In addressing mandatory voter registration, we could make registration easier, and make our voter rolls complete. Citizens with the legal right to vote would not be denied that right by attempts at voter suppression, in making elections fully inclusive of legal voters. At the same time, if we were to enact compulsory voter registration and compulsory voting, it would make sense to follow the suggestion of "Why Tuesday.org", and move voting to weekends, which also tends to increase voter participation.
Voting participation is good for the nation, and as participation declines, either through apathy or efforts at selective voter suppression, some form of mandating it as a requirement is sufficiently beneficial and far more fair to justify it not being left voluntary any longer.