Bitcoin will never be accepted as a "real" currency if it continues to fluctuate like it has in the past. Nobody wants to buy $600 worth of currency only to have it drop the next day to $480.
In my opinion, there are a select few people making HUGE money manipulating the market. There should be no reason Bitcoin rises and falls $100's (Sometimes over 100%) in such a short time.
That is true. But when the bitcoin is used more, the market cap will be high, it is more difficult to manipulate.
Indeed the more it's used the higher the cap and then people would need billions to even change the price.
But right now I guess you could manipulate it if you are very very rich.
I haven't booked profit when it touched 400$ btw, I didnt buy any sadly enough.