There are scenarios where random accounts become the biggest funder so that they get the collateral. Now users dont diversify and expose themselves to higher risk (eggs in smaller baskets). Those accounts might be controlled by the borrower.. Now collateral is useless. Collateral is in Russia, you are US based. How are you going to get that collateral? What about the other 400 investors-- what are they going to get out of this? They invested but now they get nothing? How are you going to vet the collateral? What happens if that collateral were to be devalued say in a market situation which crashes? Gold was the collateral and market crashes & the borrower had defaulted -- would that still satisfy you if you had such collateral?

edit: Not trying to be smart here, I'm truthfully just curious about the answers.