Which economically rational person buys unbacked digital assets?
Anyways, if you for example have stolen money or Bitcoins, you don't need to be economically rational. Also paying a price for hurting your competition can be economically rational.
Yes a political motivated attacker could be a problem.
Reputation system could help, but would not be perfect.
I have another idea how to solve that and will add that to the paper soon.
It leaks private data (cash in mail: mail address, bank transfer: bank account data) all over the place. I described one problem (stolen bank data which will lead to later reversed USD transactions) already, also there can be indefinite lock-ins, the extra funds at stake (in your example 10%) can lead to people implicitly taking a short/long position, it requires trust to begin with (who wants to trade with a newbie in your system?), both traders need to be online and do manual tasks outside of the system...
I mean, feel free to try this out in practice, it's not even hard to do - just post an offer in this forum for the mean time, put some funds on the table and get trading. It took less than 2 weeks each for 2 different new Ripple gateways, until they had a few 1000 USD bank transfers reversed each. Maybe you can beat them to it?
Yes you loose your privacy to the other peer, but not to any other party (in normal exchanges you loose it to the company and the state if they request the data).
You may not use bank transfers which are reversible like paypal. SEPA for instance in EU is noreversible.
Money hardness:
https://en.bitcoin.it/wiki/Payment_methodsMoney is only locked if one is too stupid to understand that cheatin in that system will only hurt both. There is no win possibility beside the fair behavior.
The collateral can be choosen freely by the offerer. And you dont need to take an offer with too low collateral.
Yes people have to do an asynchronous process. The banking system does not allow us other solutions. Sorry.
If you read the paper all these points are discussed there and the attack scenarios are layed out.