Throughout recent history, scientific and cultural changes have been subjected to the slippery slope argument. People talked about the slippery slope when the first artificial insemination was publicized in 1909, conjuring images of selective breeding and a race of illegitimate souls. They talked about it after the first heart transplant in 1967, .... There's power to the argument, because if we hadn't allowed those first steps -- the refinement of intrauterine diagnosis, the definition of brain death, the limbo created by the heart-lung machine -- the more disturbing applications could not have come to pass...
What does "power" mean here? Does the author think it is a possitive or negative power? Is the author for or against the argument?
Besides, what does "limbo" mean here? A kind of living-dead condition?
Overall, I think the author is going to turn out to be against the argument; here, however, with the word 'power', he is acknowledging its legitimacy and strength. (The argument itself may be positive or negative-- depending on your attitude toward it-- but the power of an argument itself is just that-- the power to convince.)
'Limbo': yes, neither dead nor alive-- biological systems kept functioning by a machine, where the unaided body would die.