Yes, but in this case we're talking about Windoz emulation! If you embrace this philosophy why emulate a totally closed-source O.S.?
The things are in contrast.
I like open-source and I develop my software trying using only (if possible) GPLv3 but it doesn't mean I refuse to use closed software at all.
Let's face reality: we cannot fight Micro$oft (or Oracle) empire with this attitude.
I use Windoz for my work and I cannot avoid it or I can't get paid, most of the times. But everytime I can, if a open source alternative is possible, I suggest my customer using it.
In my opinion it's not everytime a ideological battle.
And what about closed-source in Kernel?
I try to avoid this kind of discussions since I know that it's often a ideological battle and can degenerate in flames.
Simply: one is asking a question - I answer the better I can. No intent to pull who's asking to a part or another.
I'm definetly NOT an extremist and I think that freedom can be, in some cases, the choice to not to be free.

since its being discussed. is virtual box (not the extension) open source software or Free software?

Look at Virtualbox Licensing FAQ:

it seems to be Free software. if oracle decide to close the source; people can still fork what's already a quality product. I think that's how libreoffice was formed.

Exactly. Since Virtual Box is released even under GPLv2 if Oracle decide to close the source the pieces of code under the GPVv2 remains under that license.
Everyone can makes changes on it, extend it and redistribute the source to the public domain with the same license.

Yes, I will gladly wait for a true open source fork of VirtualBox complete with free addons - it will happen. Until then I will use qemu, actually I'm beginning to enjoy qemu as it's lightning fast on my machine even though it requires a bit more work. If I remember correctly, VirtualBox was forked from qemu.

As long as the name is changed.