The difficulty with the generation study is that there is no way to selectively opt in/out; your child is sequenced and then the data is retained until you opt out (at which point it is still retained as part of historical releases). It isnt ringfenced for medical research and can be accessed by pharmaceutical companies. It isnt even kept by the NHS but rather by a private arms-length body of the government which could be privatised under a change of leadership. We've seen failures with UK Biobank data security, why would this be any different?