Say a group of rich investors got together and intending to buy huge amounts of bitcoin with the intention to one day crash the market. Say they told other investors of their plan deception and they bought into the idea. They done this for a while making the price of bitcoin soar. If they all collectively cashed in on their bitcoins and told people/ warned people and fooled them into doing the same via news articles, websites and other forms of mainstream exposure. Could they theoretically cause enough of a collapse to then buy the bitcoins back at a low price and wait for it to boom again makinf a huge profit or am I totally missing the point?
The thing is buying it and trying to sell it simply does not work.
When you buy bitcoin, you drive the price up. When you dump it, you drive the price down. In the end, they are likely to incur a loss from all this and the bitcoin price remains unaffected. Only if someone mines a lot of coins and dump it all at once can it have substantial effect on bitcoin price because this is the only way to obtain bitcoin without having bitcoin go up in the first place.
The hardest part of your plan is not buying the bitcoins but rather, trying to get others to buy in. Trading is a negative sum game so to make a profit you must convince others to follow what you want them to do. This is how pumps and dumps work.