I would gladly give up my DNA to fight crime at a national level. But realistically I don't think the agencies in place can currently be trusted with this information as they already are listening illegally to everything we do. Once the governments and security agencies have won my trust back they can have my DNA. Until then no thank you.
Yes, I think that a DNA database is essentially needed when it comes to fighting crime. A DNA database would help track offenders, and help to keep all their DNA secured somewhere. I think it would also stop some of the crime since DNA would be collected of possible offenders.