That's the problem with the non collateralized loans, they need to provide incentive to the lender to take the risk, and they must remain profitable despite the occasional default. You've done a pretty good job weeding out the deadbeats, and I've had a good run as well. Even with one default I made a reasonable return in the given time frame I've been offering loans.
When offering non collateralized loans the lender's security is really up to the lender. Diligence in researching your client is key, and therefore non collateralized loans require more time invested. Another legitimate reason the lender can expect them to be more profitable. And the lender really owe's it to his trustworthy clients to keep his defaults to a minimum so he can keep his rates reasonable.
I've been using a checklist to expedite the process, while still investigating a potential borrower thoroughly. The checklist is always in progress, and I've been thinking about adding values to certain member attributes to help generate a sort of "credit score." My plan is formulating a "risk" level to help calculate a reasonable, but not too risky amount to lend. As I get better at spotting riskier borrowers, and I could mitigate the risk of non collateralized loans, lowering rates would be an obvious next step.