I wouldn't call it manipulation tbh. It's possible by nature to dump or pump the price as long as they could do it. If pumping or dumping an asset price is called manipulation, then I guess every second in the market is an act of manipulation.
I prefer to call it a free market trade. If a whale wants to dump 5000BTC at once, then so be it. No one cares about a "fat finger" when the price goes up, but oh boy, when it goes down hell breaks loose. People need to stop being so sensitive to things that happen here. If this market isn't for you, then go elsewhere.
If we want to avoid something like this to happens, then limit the number of trading volumes each person can do for each day. Limit it so that nobody can sell more than 2 BTC a day, or in extreme case, 2 BTC a week. Though I doubt that is plausible for everybody.
Stock markets have certain triggers in place that halt trading when the price tanks 10% in x period of time, which I think is a matter of time before it becomes an obligatory feature for exchanges. Not sure what I think about it would exchanges implement this tomorrow, but at least it would add more comfort to those coming from the legacy space.
