Rather than me explaining it, why not listen to John Sullivan? He's Executive
Director at the Free Software Foundation and gave a talk called State of the
GNUnion. This question was discussed during the Q&A session. I encourage you
to listen to it: http://faif.us/cast/2013/oct/17/0x43/
The Q&A starts at about 45 minutes in.
You'll hear him say "It's not that it's OK."
Someone also jumped in explaining that "there is a definitional problem going
down as well as going up."
Hopefully listening to it will clarify it.