Just like if someone didn't understand how public/private key encryption works it would be sleazy to ask them for the PRIVATE key of their wallet to deposit money and then use that private key to steal the rest of the BTC from their wallet.
That's true. However, I haven't used it to steal BTC IOUs from other people's wallet, people who have zero affiliation with me (other than also being sent my IOUs) did.
TESTING MEANS TEST IT ON MYSELF / OWN ACCOUNTS. I am not responsible for anything other people do. Oh, and see Deprived response for why Ripple is actually flawed in how liquidity providers work.