In his own reddit AskMeEverything page,
https://www.reddit.com/r/IAmA/comments/80ow6w/im_bill_gates_cochair_of_the_bill_melinda_gates/He answers about cryptocurrency stating
The main feature of crypto currencies is their anonymity. I don't think this is a good thing. The Governments ability to find money laundering and tax evasion and terrorist funding is a good thing. Right now crypto currencies are used for buying fentanyl and other drugs so it is a rare technology that has caused deaths in a fairly direct way. I think the speculative wave around ICOs and crypto currencies is super risky for those who go long.
He isn't wrong in his sense, if the cryptocurrency is to have a future, they should be able to create an environment of trust between themselves and the authorities.
Everyone is entitled to their opinion and it doesnt matter what people think, the truth is really difficult to handle and in reality we are now facing new changes in financial technology like cryptocurrency and blockchain technology. Opinions of such prominent individual like Bill Gates are alright and as long as he is not stepping out of his own limitations and as long as he's not enforcing his opinion to be followed by other people.