Mandatory voting is a good idea. It might actually tend to short circuit some of the influence of mega-dollars on elections. You could give monumentally uninspiring candidates like Hillary Clinton, who very few people would go out of their way to vote for, at least a chance if you forced people to choose. But:
1) It should be strictly by mail with ballots mailed to voters by their county clerk’s office.
2) The window for returning the ballot should be at least two weeks giving everyone plenty of time to decide and to comply.
3) Ballot return should be postage free so that no one can claim they couldn’t afford to return it.
4) Completed ballots should have nothing on them identifying the voter and should be enclosed in an outer envelope with the voter’s ID on the outer envelope only.
5) When the ballot is received by the clerk’s office, a bar code on the outer envelope could be scanned to give the voter credit for returning the ballot.
6) A post-paid postcard could then be detached from the outer envelope and sent back to the voter as a receipt and proof of compliance.
7) Completed ballots with no identifying information would then be removed from the outer envelope and placed in a bin for machine reading.
8) The machine-tallied ballots whould be kept in bonded storage for at least a year—maybe till the next election—so that if irregularities are suspected, the ballots can be re-counted by different machines or even by hand.
The paper ballots, filled out with a Sharpie and read optically, provide a traceable and recountable hardcopy. There should ALWAYS be a hard copy and we should NEVER rely on purely electronic means to count votes and store the results—that just invites hacking, tampering and “computer failure.” If that’s too much trouble, then we don’t deserve a democracy. So there.