Convicted criminals become wards of the state, but they still have rights. I don't think carte-blache DNA collection of all criminals is justifiable. The U.S. has a bloated justice system right now, with so many laws on the books, and the highest number of prisoners per capita. Conviction in of itself should not mean automatic DNA collection, unless authorities can prove that the DNA could help the justice process in the future.
My point in my previous posts is that we should assume the government is going to abuse power, because that's what governments do in their nature. Our Founding Fathers knew it, which is why the Bill of Rights is worded like it is. We have to err on the side of the rights and liberties of the individual, always.
The government shouldn't get "automatic" right to do anything. It should have to prove itself at every stage, and not prove itself to itself, but prove itself to the People.
What SCOTUS ruled was statist, plain and simple. It eliminated one more piece of discernment from the system. It has said that DNA collection is justifiable in all cases, without review. That is dangerous.