I really don't want to be rude here, but you need to look up what an incentive and a disincentive is. The whale makes money. He is incentivized to do it. He, in effect, gets decreasing returns as when you dump a load of Bancor backed coins at once the price adjusts (the equation is in the whitepaper), but still makes money. He is incentivized to dump.

You are creating a nonsensical hypothetical where the whale could have sold his entire stack at exactly the market rate. First, that doesn't exist in normal coins either. When you dump a huge stack of an asset you typically get decreasing returns, just like Bancor gives you in-effect. Second, Bancor backed coins can be traded on the open market, so nothing prevents the whale from treating it like a normal coin anyways. Finally this whole hypothetical revolves around the single scenario where a pumper can lose money. You apparently think it is impossible for a pumper to lose money. It is a good thing it isn't. The Bancor model incentivizes pumping and dumping enough already.