It is currently easier to register a vote of "no preference" than an affirmative vote. I think people should be able to cast blank ballots, but this should not be an easier vote to cast than a ballot in favor of a particular candidate.
Voting is a public good, and it is easy to shirk your civic duty while still benefiting from the overall reasonable outcomes that it is likely to produce. Making voting mandatory will prevent free riders.
Forcing people to vote will prompt them to be more involved in our democracy. Democracy is not easy, and the fewer people vote, the easier it is to corrupt the process. This then leads people to become disenchanted and believe that the process itself is flawed or uncorrectable.