Voting when the Constitution was ratified was basically restricted to white males. Freeing the slaves and enfranchising them, allowing women to vote and lowering the voting age to 21 each took individual Constitutional Amendments to bring to fruition. Until recently, though hard-fought and excruciatingly slow, the direction of change has been in favor of including larger segments of the population in our elections, not smaller ones. Without swift Congressional action, this decision by the Supreme Court could result in a drastic exclusion of increasing numbers of people from the electorate unjustly.
via The Right to Vote.