Why is less than 100% not achieving anything?

OK - Not achieving anything is the wrong phrase. My apologies. I should have said that less than 100% testing will not prevent the spread. Simply because there will always be an element who, for whatever reason, will continue to be irresponsible, not be tested, not use safe precautions and generally be responsible for spreading the virus. I also suspect that people could be lulled into a false sense of security if they feel that a testing program is going to keep them safe.

Agreed that we should be persuading as many as possible. By education, not compulsion.

Every early diagnosis is a life saved, and reduces further spreading of a dangerous disease.

Not if the person diagnosed is either irresponsible, unlucky or malicious. If it was as simple as you put I would agree but it isn't.

Cheers

DtG