If you are going to institute a system where people can take back money from someone they feel defrauded them, you would also need to build a system of justice to ensure that fraudsters don't come from the other side. eg. Someone with a significant rep comes along and starts screaming" he defrauaded me, HEY EVERYONE HE STOLE FROM ME!! about a person with a lower rep. The community jumps on board, takes whatever the fraudster says he is deserved from that person, then the fraudster makes off with the earnings of his lies. Unless there is a system to prevent this as well, then it could be manipulated. Edit Thinking about this a bit more, I guess if it is all in the block chain then there would be enough evidence to prove one side or the other, and the matter could be resolved fairly.