Re: That isn't a Steam issue.
That's not the point. I can play Mario Kart on my Wii, then take out the disk and put Zelda in. There's nothing stopping me from putting it into a Wii U and continuing to play Mario Kart there without having to shut down Zelda first.
(s/Wii/X-Box/, s/Mario Kart/Halo/, s/Zelda/BattleGearDutyCreed/ as required).
If I have two consoles running Steam, each logged in with their own account (call them "his" and "hers", just because), he can use Family Sharing to play Civilization on his Steam box from her Steam library, but will have to quit the game if she tries to play her own copy of Skyrim on hers. That's the problem.
She bought two games, and wants to play one of them on one computer and one on the other. I can't see anything even remotely approaching piracy there.