Abstract Persistent polarisation across political, social, and institutional domains has proven resistant to fact-based correction and moral appeal. This paper proposes a systems-level framework in which polarisation is understood not as a failure of belief or ethics, but as an adaptive response to cognitive and social bandwidth collapse under constraint. Treating Earth (Gaia) as the non-negotiable life-support boundary condition, the framework models human behaviour as phase responses to stress within finite systems. Emotional, social, and political extremes are shown to function as low-bandwidth stabilisation strategies, while reasoned application requires restored safety, agency, and ambiguity tolerance. By exposing both poles of polarisation as products of the same mechanism, understanding can return without confronting identity. The framework offers diagnostic tools, recovery dynamics, and policy design principles that prioritise system viability over ideological alignment.