Specifically billionaires/unchecked capitalists

The easy scapegoat oversimplifies the problem, which goes beyond & predates capitalism. Though exterminating all of humanity is one way to achieve sustainability, it doesn't necessarily require it. So far, however, humanity has reached living standards beyond subsistence only by consuming resources at unsustainable levels faster than the planet can replenish, and that has been true regardless of economic system. Even when living at subsistence levels, humanity has likely caused mass extinction events.

From a comment to a similar post

People here tend to fixate on their pet theories that scapegoat capitalism for everything including that humanity's drain on ecological resources exceeds Earth's rate of regeneration without acknowledging that their alternatives don't address the problem, either.

Although governments are far more able than individuals and firms acting singly to take action to protect the environment, they often fail to do so. The centrally planned economies of Eastern Europe, where governments controlled production, had a particularly poor record on pollution control. Per capita mortality from air pollution in Eastern Europe (outside the EU) and China remains high relative to the EU and North America.

In particular, the Soviet economy—with constitutional guarantees to continuously improve living standards & steadily grow productive forces—caused disproportionately worse ecological damage than the US's. All economic systems have the same capacity to degrade the environment & deplete stocks of natural resources. Without adequate policies to protect the environment, improving & maintaining living standards with the continuous economic growth necessary to do that threatens the environment.

Moreover, human activity before capitalism has led to extinctions of megafauna, plants, & animals dependent on those plants. The quaternary megafauna extinction was likely driven by overhunting by humans. Those extinctions & increased fires coinciding with the arrival of humanity to Australia transformed the ecosystem from mixed rainforest to drier landscapes. Aboriginal landscape burning

may have caused the extinction of some fire-sensitive species of plants and animals dependent upon infrequently burnt habitats

More recently, they killed off the elephant bird likely due to major environmental alterations & overconsumption of their eggs.

Until humanity starts living sustainably, they are the problem.