For all the talk of Ripple being centralized, they aren't by design, and they have a plan in place to reduce and eventually eliminate that centralization (to a point).
They decided that it would be a good idea to start centralized, then over time wane themselves out of the "validation" of transactions until it's in the hands of a diverse group of validator nodes where no one person has the ability to change things.
How about the part where the founders hold enough tokens that they could crash the price or manipulate the market at will. I understand that they have loose structures in place to keep them honest, but they could absolutely still act badly. We trust that they won't.
There are 2 things here, There is the cut that the founders hold, and there is the portion under the control of Ripple labs.
Ripple labs has a very strict way of handling the XRP they hold. It's not just "lose structures" in place, they are using the Ripple blockchain to escrow 55 billion of the XRP and release it on a set schedule of (I believe) 1 billion per month, and any that is left over at the end of the month is re-escrowed. So they can't just "flood the market" at any time, there is a set limit to how much they can even sell without hardforking the blockchain in their favor.
The founders have free reign on their 20 billion XRP, but I don't see why they would ever use it to crash the price.
Why kill the goose that lays the egg? I mean, if XRP is on its way out then sure, they'll add fuel to the fire, but crashing the price is counterproductive. If they really wanted to cash out and they were smart, they would drip it over time so as not to eat up the market orders on the buy side.
They decided that it would be a good idea to start centralized, then over time wane themselves out of the "validation" of transactions until it's in the hands of a diverse group of validator nodes where no one person has the ability to change things.