Both are killing our planet, they are not mutually exclusive. Capitalism kills the planet through the destruction of the environment on a global scale for profit, the abuse and wage enslavement of the working class (and the rapidly decreasing standard of living for many because of this) and the hoarding of resources for a profit at the expense of those who actually need it. Homeless people starving to death outside of supermarkets, people losing their homes from skyrocketing rents and stagnant wages or never being able to afford one because greedy corporations buy up all the homes. How can you claim unchecked capitalism isn't a scourge on our society and a root of so many of our problems?

You don't need go be a genocidal dictator to kill the planet. All you need is greed, lack of empathy, and the means to hurt people for profit.