Let us assume in a best case scenario, the Ripple system gets opensourced this year and the 50 billion XRP are distributed fairly to many people in the world.
One of the reasons of having XRP currency is to prevent spam and provide safety to the Ripple network from abusing.
OpenCoin has about 50 billion XRP or even 30 billion XRP without the founders count. So they can technically use their massive XRP to harm the system if they need to. I have not reviewed how many different and harmful ways one can abuse the Ripple network if they have too many ripples.
Why does any single entity needs to have such amount of power over the network? Technically, for us to trust Ripple, we need to trust the OpenCoin entity forever. Even if OpenCoin people are good, what if their accounts got hacked and the XRP is with malicious people?
PS:
Got downvoted on stack exchange for asking this
http://bitcoin.stackexchange.com/questions/11821/how-exactly-is-ripple-decentralized-when-opencoin-has-the-power-to-abuse-the-rip
