Under Swiss Law (FADP 13) the processing of personal data is only lawful if it is justified by the consent of the person concerned, by an overriding private or public interest or by law. Examples of such an overriding interest are listed in FADP 13 II. Such an interest may exist in particular if personal data of the contracting party are processed in direct connection with the conclusion or execution of a contract.
With regard to consent under FADP 13, however, I am of the opinion that not every processing of personal data is permissible if the person concerned agrees to it. Digital platforms, such as WhatsApp, make their users disclose almost all possible data about themselves, since the benefits of the platform are so great for the persons concerned or, if they refuse, e.g. they are cut off from their social contacts. In addition to the principle of proportionality (see below), I believe that Swiss Civil Code, CC 27, also applies here, through which the state protects those affected from themselves, so to speak. According to this rule, one «cannot renounce one’s freedom», i.e. one cannot «enslave» oneself to third parties.