A currency needs fungibility needs privacy. Here are two quotes from Andreas M. Antonopoulos’ Q&A.
I think the biggest weakness that Bitcoin has is that the base layer – the first layer blockchain – is insufficiently private. […] That threatens the currency’s fungibility. – https://www.youtube.com/watch?v=O_YgFzgAw8w#t=3m46s
If cryptocurrencies start getting attacked using privacy as the attack mechanism […] any cryptocurrencies that do strong privacy immediately become much more valuable. – https://www.youtube.com/watch?v=O_YgFzgAw8w#t=12m59s