To mark the 50th anniversary of the signing of the Voting Rights Act, here's a quick quiz:

State A offers early voting and absentee ballots to all who are registered, allowing voters to cast their ballots before Election Day. State B does not. Which state is being sued for violating the Voting Rights Act?

If you answered state B, you flunked. Now you see the problem with today's debate over voting rights.

In 2013, North Carolina (state A) passed a law reducing the number of early-voting days while maintaining the number of early-voting hours. It also ended Election Day registration, preregistration for those ages 16 and 17, and out-of-district voting, and it required voters to show photo identification at the polls.

The Department of Justice filed suit, alleging that the law violates the Voting Rights Act by denying or abridging the rights of black Americans. Under the new law, the state's minority voters continue to have more opportunities to cast ballots than minorities in other states — including New York (state B). So why isn't New York — which doesn't offer Election Day registration, preregistration for youth or out-of-district voting — getting sued as well?

In practice, violations of the Voting Rights Act occur only when states limit voting opportunities, not when they fail to expand them. States that liberalize their voting laws and then attempt to rein them in, as North Carolina did, run the risk of violating the law, while states that always have had strict requirements on registration and voting, such as New York, are free and clear as long as they don't make those requirements any stricter.

That distinction makes no sense — and the revision of the law that Democrats are pushing wouldn't put this right. It would merely restore the requirement, struck down by the Supreme Court in 2013, that states with a history of voting-rights violations submit any changes to their election laws and procedures to the Justice Department for prior approval. That would affect only a handful of mostly Southern states, many of which offer more voting opportunities than some Northern states.

A more forward-looking approach to voting rights could usefully address another issue. Laws in New York and other states prohibit independents from participating in primary elections. That exclusion, some argue, is a voter's own choice — but why should voters be forced to join a party to participate in elections that are funded and organized by their own government? Equal access to the polls, regardless of party affiliation, should be a voting right, too.

Voting rights are universal, and they should be universally protected. There's still a need for a robust Voting Rights Act. But those leading the crusade for changes should aim to treat all the states — and all kinds of voters — equally.