Edit: Now I’m seeing the Code ruling on cargo. I assume the free action of transferring crew wouldn’t be enough to voluntarily eliminate crew from the game either.
Voluntarily is the key word. Essentially, you can’t do anything on your own that would force an illegal situation, which in most cases means you simply cannot use whatever ability or rule would cause it.
It has to be triggered by an opposing player, or some outside force that you can’t directly control, like a UT found when first exploring an island.