I can understand wanting to save energy, I'm not saying PoW is perfect either. But no one can seem to explain to me in simple terms how PoS is supposed to stay secure without mining.
If the higher stake gives you preference to perform security duties for the network, get rewarded, and stake can be purchased with fiat which is unlimited and unsupervised...what kind of security is this?
How can we even think about preventing the people who have access to printing unlimited money from taking over and voiding the security to rule out the competition?
With unlimited money you could easily bribe miners too. Dan blogged about POS security a lot, he said that there was a way to prevent someone from taking over the network ( don't remember exactly how, you will have to search through @dan @dantheman's posts if interested).
Also ethereum POS is coming soon , so we will see how they protect a 4 billion network against corruption...