Why Ethereum Ditching Mining Isn't as Green as Advertised

This argument doesn’t hold water for several reasons. Firstly, unlike in PoW, a cartel controlling more than half of the stake can silently, invisibly, and permanently capture the entire network. Secondly, an attack on a PoW chain is in the first place less likely than an attack on a PoS chain. It’s easier to attack a PoS chain because doing so doesn’t require scarce assets like hardware or electricity. Actually, it doesn’t require staked assets either: the attacker only needs to acquire keys of former validators, or very briefly operate a huge number of validators (anyway a profitable enterprise). With these keys in hand an attacker can carry out a long range, costless simulation attack, which would produce a blockchain that for all practical purposes appears equally valid to the canonical chain.