Most of these people will be working in a controlled environment with little or no opportunity to pose a threat to children. Of course safeguards must be in place to try to protect children where employees and others have unfettered or unsupervised access to children – and I believe it already exists in the form of enhanced CRB checks.
There is also a grave danger that people will be incorrectly labelled as “unsuitable” by this process. For example, it is likely to “fail” people who have been arrested, but not charged or convicted of any offence, but who happen to have their DNA profile taken and illegally (according to the European Court) retained.
A far greater threat exists in the form of single mothers who allow strange men unrestricted access to their homes and children simply on the basis that they have known them for a few weeks (or sometimes even less). No checks are carried out on their backgrounds and they have the potential to inflict far greater harm upon children than, say, a seventy year old lady who volunteers to do a bit of work at the local nursery once a week.