Should the US have mandatory voting?

[MarkD]

To borrow an idea from George Will -- if government forced me to vote when I don't want to I might turn pretty cynical and purposely vote for the worst candidate(s).

No way. No mandatory voting. Uh-uh.

[MarkD]

There should be a tax credit for voting and a tax penalty for not voting IMO

How would that be different than a poll tax, the kind used in the Jim Crow South, except in reverse.

Some countries, like Australia, fine people for not voting

If anything...a tax penalty for not voting is probably more efficient than giving people a fine

Muon 2 was not just making a moral point about the wrongfulness of imposing a poll tax. The U.S. has two laws that we cannot impose any tax on a citizen as a prerequisite for letting them vote. Those two laws are: 1) the 24th Amendment to the U.S. Constitution, 2) the Supreme Court's precedent in Harper v. Virginia Board of Elections, 1966. Australia and other countries do not have such a difficult-to-repeal-law that prohibits poll taxes.

Absolutely not.

[MarkD]

I wish voters had to pass a test on basic US government, history, and economics to register. Obviously that's not constitutional, but enough of the electorate is already uninformed without mandatory voting.

I don't think the kind of test you're referring to is "not constitutional," I think it's illegal per the Voting Rights Act. When the Supreme Court was faced with a literacy test for voters, it unanimously upheld the test (Lassiter v. Northampton County Board of Elections) but years later Congress banned literacy tests for voters when it passed the Voting Rights Act.
https://en.wikipedia.org/wiki/Literacy_test