Materialists posit a universe where every aspect of reality has a physical, mechanistic explanation. Physical pathways connect cause and effect; chance plays a starring role, but it comes from quantum unpredictability, not God or human agency or “wonder tissue.”
The implied determinism may be difficult for activists to swallow. Why work to effect change if outcomes are predetermined (at least partially)? If the universe is a math equation, what’s the point of trying to balance a few odd remainders?
An answer, I think, comes from subjecthood. The experience of consciousness—your values, thoughts, perceptions—is profoundly unique. And regardless of who or what is drawing the causal arrows, it’s a two-way experience; the photons your eyes absorb aren’t absorbed elsewhere. One’s simply being alters the makeup of everything, however imperceptibly.
Environmentalism needs subjects. The universe may not care, but subjects should.