This is an idea I intend to elaborate upon in time. People concerned for the authentic human good (and I believe myself to be one of them) see things as being on a slippery slope. First, abortion becomes legal at a time when most people considered it an abhorrent crime. Then, people begin accepting it. Then, it becomes a right. Then, we start killing off our old and infirm. And then what? Where does it end? We're going down a slippery slope.
There is a certain validity to that notion. But it is ultimately a matter of perspective.
If you want society to head toward a eugenic weeding out of the poor, sick, and useless, and have had a hard time in the last century or so garnering public support, you start slow. You get people used to an idea. You push it a little farther. Then a little more. Soon, you'll have everyone clamoring for what you want to achieve.
But, I think the whole eugenic thing is also only part of the puzzle, and although its proponents think about improving the human race in some way, I think there's an ancient mastermind behind it who just want us to get used to killing "the unfit," and the definition of "unfit" will eventually refer to the class of naysayers who stand in the way of Progress. Ultimately, it's about killing off the human race altogether, or warping it beyond recognition and replacing it with something else, something not essentially ordered to God but to some other thing. In the lore of Middle Earth, the Orcs began as Elves, and were twisted and manipulated into evil creatures.
So I think the slippery slope is a myth. For those who support things like euthanasia and abortion and all manner of death technologies, it is not a slippery slope at all, but a well mapped expedition. The so-called "safeguards" to prevent things slipping further are just lip service to lull naysayers into complacency. We call it a slippery slope, but they sit back and say, "Everything's going according to plan."
More on this when I can.