Yes, a down/uptrends trends market is necessary on the crypto market because traders/investors must book profit, and this is the demand and supply principles playing out on a regular intervals. There are traders/investors that must sell, that is, a supply entrance into the market , while there are traders/investors that will buy these supply that is entering at certain price rates overtimes.
In fact, there must be ups and downs constantly, it is a normal market movements, which involves buying and selling of assets everyday.