The justification is that contrarily to PoW, where there are economies of scale on computing power, PoS power scales linearly with your stake.
Mining has been concentrated in the hands of a few gigantic mining pools for a while, and PoS will actually make Ethereum more democratic. Again, this is based on documentation, there might be unforeseen consequences
There are no economies of scale in PoW. At least for longer term. Cost of energy rises locally the more you use it. Cheap energy is somewhat equally distributed around the globe, which ensures geographical decentralization.
This has more to do with electricity demand. It's important to understand the relationship between energy price vs. population density and standard of living. Energy is always cheapest where population density and standard of living are the lowest. That's why bitcoin mining will find it's way to remote sources of natural energy.
