I think having a DNA database can help with the fight on diseases, there are so many diseases that have genetic links, and having a database can help with research in discovering medications or treatments in helping with the diseases, so I think its a good thing to have a DNA database.
I don't think a national DNA database would do anything to fight disease. All it would do is make a big database of DNA information that people could, theoretically, look at. I don't think anyone could actually use that for a good purpose. Just knowing what gene someone carries doesn't make disease go away.