Treating your personal data with the same care as the medical professionals
Being of the appropriate age group, I did receive an invitation to join Biobank. As I recall, although they did promise to try very hard to keep your data safe, they were honest enough to admit they couldn't control the future and that courts or a future government might overrule them.
And that's the problem - it doesn't really matter how much you trust people with your data now, it's what will happen to that data in 10, 20 or 30 years time that's the issue. So, it would be careless to give it away in exchange for information you could glean simply by looking in a mirror.