It's actually dealt with in the preface/introduction of the book. Firstly culturalism is defined:

In this work, I propose a critique of what can be called "culturalism." I define culturalism as an apparently coherent and holistic theory based on the hypothesis that there are cultural invariants able to persist through and beyond possible transformations in economic, social, and political systems. Cultural specificity, then, becomes the main driving force of inevitably quite different historical trajectories.

Then modernity is critiqued.

Modernity is the product of nascent capitalism and develops in close association with the worldwide expansion of the latter. The specific logic of the fundamental laws that govern the expansion of capitalism leads to a growing l inequality and asymmetry on a global level. The societies at the peripheries are trapped in the impossibility of catching up with and becoming like the societies of the centers, today the triad of the United States, Europe, and Japan. In turn, this distortion affects modernity, as it exists in the capitalist world, so that it assumes a truncated form in the periphery. The culture of capitalism is formed and develops by internalizing the requirements of this asymmetric reality. Universalist claims are systematically combined with culturalist arguments, in this case Eurocentric ones, which invalidate the possible significance of the former.

The crisis of modernity is itself the sign of the obsolescence of the system. Bourgeois ideology, which originally had a universalist ambition, has renounced that ambition and substituted the postmodernist discourse of irreducible "cultural specificities" (in its crude form, the inevitable clash of cultures). As opposed to this discourse, I suggest that we begin with a view of modernity as a still incomplete process, which will only be able to go beyond the mortal crisis it is now undergoing through the reinvention of universal values. This implies the economic, social, and political reconstruction of all societies in the world.

The universalist values (such as LGBT rights) got undermined and invalidated during colonialism, the only way to move forward is a redefinition of universal values from a non eurocentric point of view, not rainbow capitalism/imperialism.