The first option, "the use of the personal information in a way that would discriminate against individuals based on confidential information such as potential genetic diseases," would be considered a "con" to having national DNA databases. It highlights the potential for misuse of sensitive genetic information, leading to discrimination or privacy concerns.
The other options, such as "the irrefutable evidence of a person's unique DNA," "the gigantic size of the database," and "the solving of cold cases," do not represent cons. Instead, they refer to the evidential strength, logistical challenges, and potential benefits associated with national DNA databases, respectively.