How you will make people pay back the loan?
The key (which has been an underlying principle of the CU movement for over a century) is that the members are connected by a common bond. Thus, if you default on a loan from an institution that you and the peers whose respect you value cooperatively own, you will be forced to deal with the stigma of essentially stiffing your friends/co-workers/project collaborators, etc. Thus, a member of a credit union with a tight common bond can often be expected to go above and beyond in attempting to pay off their debts in order to avoid the judgment of others...
Also, loans are distributed among members who choose to invest in the loan so that it is less of a risk to everyone. This, with a trust system built into the site let others know your trust rating, giving the investors an idea of the risk they are taking when they invest in a loan.