Proof of stake seeks security without cost,
but the laws of economics say that security
costs will always rise to meet the rewards...
Laws of Economics are not universal, they are environment dependent. Change environment (this is what cryptos do) and you will change the laws.
Right now we observe that there are some PoS systems that consume almost no electricity but have not been successfully attacked yet (and the
reward is very appealing). Your statement contradicts to observations and this makes me suspect that you are wrong...
...And if you don't want rewards to secure the
system, then you'd be taking away one of
the most important aspects of Bitcoin's security model,
which is incentivizing people to honestly participate
in the network instead of attacking it.
Noone proved that Bitcoin's security model is the only viable one.
not sure if you mean reward as in block reward or just the fact that alts have a market value.
eventually Bitcoin will run only on transaction fees, similar to how nxt does it now, in that the
security cost will become equal to the transaction fees in both cases (unless you don't believe
people will try to game the system to compete for maximum profits).
So, then the question becomes: what is the security cost during the issuance phase?
While it may be true that a major PoS alt hasn't been successfully attacked,
we don't know if this approach can scale or that people want it.
As others have said, these alt coins already exist, so all we need do
is wait and see what unfolds. if the PoS system is indeed viable and superior
as some claim, we should see it start to gobble up market share...right?