DNA testing not only helps law enforcement accurately identify criminals, it can also be used to exonerate the innocent. The tests being used in the criminal justice system works in very much the same way a fingerprint works. The tests do not reveal any type of physical traits or medical information. It is simply a means of identification that has been proven to be 99.99% accurate. The use of DNA testing has helped identify unrecognizable remains. It has helped solve cold cases. It has helped law enforcement to bridge the link between criminals and criminal cases. According to the Federal Bureau of Investigation, CODIS (the dna database) has produced 315,410 hits and has assisted law enforcement in 303,201 investigations, since December 2015. For states that have passed laws to allow for post-conviction dna testing, statistics are showing significant improvement in solving criminal cases and freeing the innocent.
DNA databases are a good idea because they show accurate factual information. Even if they have the DNA of some one, they are not going to do anything with it. If the US had any sort of technological security, they would be able to block people that try to tamper with the system. DNA databases are just another source that can prove the point accurately 99% of the time.
Collecting and maintaining a DNA database of criminals might help solve a few crimes, but it is also an invasion of privacy on a massive scale and not worth the small benefit it may offer. To forcibly collect DNA from people and store that data to use against them is a dangerous principle and one that opens the door to more and more loss of privacy. If the police have a legitimate reason to get someone's DNA they can get a court order, until then DNA should remain private as it is part of someone's body.
A DNA database would not help the accuracy of the justice system. First it would be invasion of privacy for all the people that have no need to have their DNA on file. It will also open the way for people to tamper with the system and cause more problems.