P.S. If you take it to the extreme and have a PoS coin with no fees to fight over, then
you have zero sercurity cost, but what incentivizes nodes to even participate in
the network at all? Well, "stake", one might say. But the problem with that
is it then makes more sense to attack the network than to participate
in it honestly, since there's no rewards.
Because PoS systems have no capital requirements for security, they depend entirely on marketing and have nothing to benefit from grassroots startup. Fifth Avenue will have a new industry for which to develop advertising markets. The only PoS systems that will see any success will be backed by central banks and large corporations. The network attacks will be the advertisements bombarding every form of media.
It will also require something to back it because there is no incentive to invest in a commodity that cost nothing to produce. Banks will back them with worthless junk derivatives and promissory notes. They will become fiat currencies and as such become politically charged. PoS will become state sponsored and inflatable.
In a nutshell, PoS is little more than a technology to support fiat currency.