Actually it would do away with 75% of the Democratic Party's base, which is why Democrats would oppose such a requirement.
That would depend greatly on how much power the Democrats have over the manner in which such a requirement is crafted and applied. This is exactly the point—the
“literacy tests” of old were specifically crafted and applied to disenfranchise that those in charge of these tests wanted to prevent from voting, exactly as the Democrats would do with any such test of they were allowed to apply it today.
In a state such as California, which is thoroughly ruled by hopelessly-corrupt Democrats, do you really believe that any
“civics test” imposed as a condition of voting would not be blatantly crafted and applied in order to disenfranchise Republican/conservative voters?