I'm learning about Article 14 of the ECHR and am a bit confused by the practicalities of its application. I understand something must fall within the ambit of another Convention right, and that there must be discriminatory treatment between two comparable groups (or a lack of justification for equal treatment among reasonably different groups).
I further understand, however, that the discrimination is lawful if it is both A) proportionate for the purpose being addressed (ie it doesn't unduly restrict individual freedoms in light of the goal being pursued); and B) is in pursuit of a legitimate aim (ie protection of health).
Suppose Parliament passed a law saying that individuals suffering from disease X, which is no more contagious than other sexually transmitted disease, cannot have unprotected sex. I understand this would likely be an Article 14 violation in light of the Mohammed Dica case, which states that individuals may consensually run the risk of giving another individual an STD, so long as it is not their intention and there is informed consent of that risk, etc.
Could the government justify the difference in treatment on the grounds that "preventing the spread of disease X" is a legitimate aim (protecting public health), even though they have not imposed the same restrictions on those who suffer from any other disease which is equally or more contagious? Or would this fail to be legitimate/proportionate given that such a justification is arbitrary discrimination in that it doesn't provide any justification for the departure from the treatment of similar groups? If it would indeed fail, which principle (proportionality or legitimacy) would be violated?