Let me again say it's not the return that matters to most of the posters here - it's the misdirection, changing of terms, lying about collections, lack of transparency and over lackadaisical attitude of Prosper.
Not me. I care about the return first and foremost. And there is a risk component that affects the return. The other items you mentioned " the misdirection, changing of terms, lying about collections, lack of transparency and over lackadaisical attitude of Prosper" are all issues that affect risk.
I'd say that risk and return matter.
However, when what we can see is Prosper being careless in observing their contracts, posting average ROI figures that are way off, having misleading advertisements, being capricious in treading on lenders who are following the Lender's Agreement, and banning those who bring to light fraud that Prosper would otherwise not act on, ignoring warnings that lenders bring to their attention of borrowers who are basically posting in Prosper's own forums that they intend to commit loan fraud, how can we then believe Prosper when they tell us to trust them?
While I got roughly 10% return on my investment after all is said and done, I consider the risks too great to consider investing in them again because of Prosper's past behavior.