It's not controversial in the traditional sense of the word, as in hardly anyone objects to it being used, with the exception of those who think its growth is unsustainable either in value or scaling. It did get some notoriety from use in illegal markets and ransomware over the time, then again, it creates more exposure and it's not something that couldn't be done through conventional means.

Governments have had a hard time catching up and dealing with the decentralized and anonymous nature of it, which has led to some premature bans. However, it's absurd to attempt to regulate and enforce the use of private keys in encryption algorithms. At that point the controversy should be about government overreach and not Bitcoin or cryptocurrency in general.