Without God, humans are no more than accidents of the universe. On what basis should you, a bundle of cells, respect any other accidental bundle of cells, especially if it is going to cost you something? Loyalty to the human species as a whole might have some rational basis, but why be truly concerned about denying the freedom of other specific individuals?
Why worry about the vulnerable, as long as we are not one of them?
Why worry that those who inhabit our planet in 150 years’ time may have to live underground to escape the heat, due to our inaction? Without God, at best, some of those people may be bundles of cells genetically related to our cells, but none will be personally known to us. (God Exists – So What?)