With bitcoin, the actors are whoever has the best price on power and the best ASICs. There's no way to know whether or not such actors will collude and, today, they're all controlled by the government of China should it choose to exercise such control. By contrast, Ripple's consensus algorithm is not inherently centralizing in this way. It won't decentralize itself, but it's possible for it to be, and remain, truly decentralized. Ripple is committed to making this happen and has absolutely no incentive not to make it happen.
RE: FCK/YOU Money: The Rise and Fall of XRP