I'm NOT supporting the OP, but I thought that maybe what's he's saying is somewhat similar to the following position: according to some basic principles of economy (at least as I know them), all resources are limited. Therefore, by taking up enough resources to "just exist", you may prevent someone else from existing, essentially "killing" them - because there's not enough resources for two of you. Alternatively, if you consider a larger scale - because economic resources in the world are limited, the USA has one of the wealthiest middle classes in the world, while millions of people in Africa are starving to death, and those who don't are suffering from diseases that could easily be cured by advanced US medicine.

But (an important "but"), first, while resources are limited, there may be enough for all of the humanity (probably; at least that's what I think, maybe I'm wrong), so by using some resources to "just exist" you're not killing someone else because they still have some resources to just exist as well - so in terms of individuals this logic may, maybe, apply to billionaires but not to people who "just exist"; and second, it's not all that simple, and while there's some "grain of truth", the real world is a bit more complex.