This is one of the more damaging decisions of the Supreme Court, setting a terrible precedent. The issues were set forth well by Justice Harlan, whose dissenting opinion is correct. Unfortunately, the majority did not agree with him.
What all of them seem to have missed, including the litigants, is that the issue not just whether grand jury indictment is part of "due process", guaranteed by the Fifth and Fourteenth Amendments. The Fourteenth also provides:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States;
This language was made the opening statements in the Fourteenth for a reason. They were not without force and effect. They were intended by the framers of the Fourteenth to extend the jurisdiction and protection of federal courts to all rights recognized by the Constitution and Bill of Rights against actions by state government.
First, "any law" includes the state constitution, which is its supreme law, subject to the U.S. Constitution.
Second, "immunities" includes all those rights recognized and protected by the Constitution and Bill of Rights, including those of the Ninth and Tenth Amendments. The framers of the Fourteenth used "immunities" because the rights recognized and protected by the Constitution and Bill of Rights are rights against action by government, which are "immunities", as distinct from nonvested rights of business.
If there is any doubt as to what the framers of the Fouteenth meant by their words, here are some more of their words, taken from debates in Congress and the press during the drafting and ratification debates on the amendment. See "Intent of the Fourteenth Amendment was to Protect All Rights", by Jon Roland.
From the legislative history of the Fourteenth it should be clear that all of the rights recognized by the U.S. Constitution are not only rights against state action, but that the Fourteenth Amendment authorizes Congress to legislate protection of such rights against state action, and grants jurisdiction of the federal judiciary over cases between citizens and their states involving them. Among those rights are the right to keep and bear arms and the right to a grand jury indictment. While the Supreme Court might reasonably have confirmed this in any given case by only declaring such rights as are minimally needed to render a decision, it is important that they not fail to do so for all the rights that are issues before the court, and the precedent of the Hurtado case needs to be reversed.