i think the biggest disadvantages of bitcoin :
bitcoin can be controlled up and down in the floor . This is a difficulty of a trader .
Currently the price stands between 5k to 6k so it is easy for traders who don't expect much margin of profit.
Yes Bitcoin can be used for buying illegal drugs etc thats why Some Govt put it Ban.
It's a Cryptocurrency newly built for Digital people, so after 1 to 2 years we all can know about it, since in this year a lot of changes occured in prices.