The environment, if the reports of the electricity usage of BTC are accurate.
This is very similar to mineral mining in the physical world: a small number of people create immense wealth while leaving huge costs of environmental destruction to the rest of us.
There is a good chance that they will be stepping on the necks of the people who are buying Bitcoin now. Bitcoin is still a zero sum game.
Its more along the lines of - whose tea and coffee did they pour salt in?
Its incredible that for a tech related site like HackerNews so many here are salty about people getting wealthy off technology.