Conservative doesn't mean what you think it does. Conservative means not changing the state at all. Capitalism is the status quo. Communism is something new, something untried, that resolves to break the status quo. Conserving the environment means to stop whatever actions we are doing to change it. Usually people mean stopping the destructive actions towards the environment, so it has eventually come to mean saving the environment/biodiversity, etc. That still doesn't change the meaning of the word conservative, which means upholding the prevailing state of things.
If a train is heading towards a cliff, hitting the brakes is conservative in the literal sense
Using your example, letting the train run is conservative, and hitting the brakes to stop it (changing the state) is radical.