Without the establishment of a comparable (in terms of barrier to entry and ease of use) privacy respecting alternative, the complete disappearance of cash is a problem. I don't use it for many transactions myself, but others should absolutely have the right to opt out if they so choose.
The central issue is control. I'm happy to use EFTPOS but would definitely not want to see cash disappear as it's not something governments can easily track and/or move.