Is there any good reason why C++ namespaces are "closed" in D?

[Walter Bright]

My issue is you're presenting solutions. But I have no idea what the problem is, 
because every time I present a solution to the examples you give, you say it's 
no good, because your problem is something else.

I cannot reverse engineer what the issue is from your proposed solution.

My second point is that changing the language is a last resort solution, not a 
first resort.

Thirdly, C and C++ are loaded to the gills with 
seemed-like-a-good-idea-at-the-time solutions that turned out to have bad 
unintended consequences that bork up the language for everyone down the line. D 
has some of those, too.

Forgive me, but:

    extern (C++, "ns")

has a definite smell about it of something going awry, and the idea that it 
shouldn't introduce a scope because nobody relies on C++ namespaces being in a 
scope despite that being the whole point of namespaces is a giant red flag of 
something terribly wrong somewhere.