I contribute nothing to the whole existence of the human race really, I'm a pure consumer. I don't produce resources, I don't create new technologies, I don't save or help people like doctors, firefighters, social workers... all that. Earth is probably better off without me.
I eat stuff not only because I need nutrition to survive, but mostly because I enjoy great food. I take 20 minutes showers everyday, and I wash my clothes every week, a total waste of water to clean my insignificant little me. I also consume countless plastic products that will probably be in some landfill long before I'm dead and decomposed. Not even mentioning the waste I produce that got flushed down the drain into the ocean.
I contemplate on the meaning of my existence and I find none. I work for a game company, we produce games that entertain people. But I'm sure the human race will continue to evolve if no one ever plays our games. I'm not even involved in the actual game asset production or programming, I have no tangible contribution to the game.
Considering how meaningless to humanity my work is, I have nothing to justify. I actually need a car to drive to work.
I draw stuff, but that can hardly be said to be worth anything, certainly not the resources I consumed yesterday.
So overall, my contribution to society doesn't justify my consumption of resources. Someone shot me dead and saved the planet!