[xigoi]

How else would you know that “cout” is std::cout and not some other cout? /s

[dataflow]

Are you sure every name in std is as unlikely to collide as cout? What about format(), apply(), ...?

[xigoi]

If a name collides, nothing prevents you from explicitly qualifying it.

[dataflow]

When it silently changes the behavior you have no idea there was a collision.