Bitcoin allows money to be sent anonymously across a peer-to-peer global network, with no intermediaries needed to validate or process transactions. That has made it attractive to those who want to keep their identity secret, including those buying and selling illegal goods and services on the internet.
Technically, the advantage of bitcoins which is anonymity and freedom is also its weakness as well. Anonymity brings about more illegal activities, which is more of a moral disadvantage, while the total freedom brings about unregulated price ups and downs, which is a economic disadvantage.