Background: The concept of legitimate interests as a basis for the lawful processing of personal data occupies a unique and vulnerable position in international data protection law. The GDPR formally adopts this concept under Article 6(1)(f); however, its operationalization raises fundamental questions regarding the adequacy of the doctrine of proportionality in protecting informational self-determination as a human right under Article 17 of the ICCPR and regional human rights instruments. Methodology: This article employs a normative juridical method integrating international human rights law analysis, the doctrine of proportionality, comparative legal analysis, and doctrinal analysis of judicial decisions. Purpose: This study critically examines whether the formal proportionality model underlying the legitimate interests framework in the GDPR can protect fundamental rights under conditions of radical informational asymmetry, surveillance capitalism, and data colonialism that characterize the global digital economy. Findings: The analysis shows that the GDPR proportionality model, although sophisticated, contains structural weaknesses when applied to diverse socio-economic contexts. The proposed framework consists of a mandatory three-step test, a Legitimate Interests Assessment (LIA), an anti-catch-all doctrine, and an allocation of the burden of proof based on international human rights law. Originality/Novelty: This article advances three arguments: first, the normative uncertainty of the GDPR legitimate interests clause challenges its adequacy as an international model; second, the transplantation of a proportionality-based balancing model without adequate institutional prerequisites risks creating accountability gaps; third, in the context of surveillance capitalism as data colonialism, a rights-first proportionality framework is required.