The problem is more of a slippery slope problem than the immediate case being made.
As stem cells become more useful, the demand for stem cells will also increase. Thus, we first let the embryos grow further in order to harvest more. However, since growth can only occur so far in a petri dish, the "term implantation" will occur so that the growth can be harvested for stem cells and other parts as well.
Most Monty Python references are crass and yours is no exception. Instead, I suggest:
Slippery sloap arguements are usually lame.
Using remains in medical procedures is a settled issue in my book. The only thing else to do with them is dispose of them.