> In another respect a two month old baby is not *viable*.
Sure he is, unless you left him poutside on the lunar surface. A two-month old baby is generally in a perfectly normal environemtn for a two-month old baby. But a sperm and an egg doign their little dance in a test tube... this is *not* normal, and the result of their union is *impossible* to be viable without direct *technological* intervention. Feeding a baby is a perfectly natural sort of thing to do. Using a pipette and a microscope to scoop up a few cells and then implant them intop a womb is *not* a natural sort of thing. It's the sort of thing that would *never* occur by way of instinct or low technology.
> Where does one draw the line?
In this case? When the embryo is put into it's natural environment. But an embryo in a test tube is as viable as *you* stand buck naked on the surface of Mars with nothing but a scuba tank and a wool blanket.
I'm not talking about some ridiculous argument of being put in a human hostile environment. No adult would be able to survive those conditions, either. A two month old in any earthly environment would not survive long on it's own. In that respect it simply is not viable. And what's a *prefectly normal environment*? The desert? The arctic? The jungle? They're all *normal* environments at different places on the earth. And how many adults could survive long in those places on thier ow, either? The argument of the baby's being to *survive on its own* is a pretty weak one.