If the State could ensure all criminals were convicted 100% of the time, but at the cost of the total loss of privacy of all other civilians, would it be justifiable?

This was a question I was asked in my Law interview. Some knowledge of the main human rights instruments is useful but not essential. It would help the candidate here to have read Tom Bingham's 'The Rule of Law' which explores several tenets of the core concept and discusses key legal principles, proportionality being one of them.There are two key limbs to this question. The first is the question of justification and the second is the question of whether the measure is 'necessary'. As with many of the rights enshrined in the European Convention of Human Rights ('ECHR'), the right to respect for private and family life, home and correspondence (Article 8) is not absolute and can be subject to qualification if the measure is 'necessary'. The mass surveillance in this context could arguably fall within the third justification in Article 8 ECHR: the prevention of disorder or crime. While, the initial question does not give any indication as to whether crime rates are likely to go down as a result of its adoption, we can infer that crime rates are likely to drop if every person considering committing a crime knows they will get caught. As noted by several studies, it is the celerity and the certainty of punishment which serves as an effective deterrent and not the severity of the punishment itself. Therefore, we can say that the justification element of the question is fulfilled.The second limb of any human rights issue is whether the measure is 'necessary'. This can be sub-divided into two further limbs: reasonable and proportionate. It is on these grounds that this measure should fail. As is now generally accepted, the mass surveillance which was carried out by the US in the wake of 9/11 was no more effective than targeted surveillance which only interferes with the Article 8 rights of a number of suspicious individuals. Therefore, the measure is not reasonable since it is not effective. On the question of proportionality, it simply cannot be said that a measure which sacrificed every individual's privacy is proportionate, even if it is adopted for noble reasons. The vast majority of individuals would be sacrificing their Article 8 rights for the sake of a tiny minority of criminals; such an indiscriminate approach would be a disproportionate violation of all law abiding citizens' human rights. Therefore, I would argue that such a measure could not be justified.