I love that analogy. No, you're not going to personally save the world by reducing your carbon footprint. But you know what you are going to be? One leaf on a tree in a forest, making that little bit more oxygen that helps collectively make the world a better place.
And that's worth doing. Especially if you can encourage other people to be leaves too.
While true in theory, you only have so much effort to give. The capitalist/bureaucratic system is designed to exhaust us, to make free time feel like a waste so we have no time to reconsider our economic position and restructure our lives to benefit each other. Avoiding capitalist middlemen that can upcharge us and shape our cultural/material reality into something that gets us to contribute to the current oppressive structure.
The propaganda-cultivated sense of moral obligation to laboriously do some tiny individualist good by reducing your carbon footprint through consumer choice is meant to exhaust you and distract you. It doesn't just shift blame, it expends your willingness to put effort into saving the planet in a way that doesn't harm BP's bottom line.
There are so many ways to benefit the planet that benefit you: saving money eating delicious vegan meals at a community kitchen (prepared with care by some of the best cooks in your community), getting access to better quality tools and appliances because your community has a well-stocked tool library and you can just borrow what you need for a fraction of the cost, decreasing medical waste by unionizing/protesting/rioting/revolting until you get high quality preventative healthcare, building/rebuilding neighborhoods to be walkable with high quality public transit to increase your physical and emotional wellbeing while decreasing emissions, or countless other options.