It's a little more complex than just worrying about cout and the potential for its duplication/collision.
In fact if cout was the only potential conflict then the criticism associated with 'why not use using namespace std' would be valid because I don't think too many people would dream up 'cout' as any sort of useful name.
If you visit https://en.wikipedia.org/wiki/C%2B%2B_Standard_Library you will get an idea of the vast scope of namespace std and hence the real potential for conflict - std is not just cout, cin and a couple of others!