Why do we need an analogy for legalized abortion?

Returning to the question of analogies for legalized abortion, Greg Popcak asks:

No analogy is ever perfect. All analogies are “good enough.”  In fact, searching for a perfect analogy is a common rhetorical device used to delay responsibility for making change.  Thirty years into the abortion debate, it is at least time for us to agree on an analogy.  What is abortion MOST like?  And what action steps are required by that comparison?

In the end, we can’t settle for the analogy the makes us comfortable.  We must settle on the analogy that most accurately—albeit imperfectly—approximates the reality.  And we must, then, act in accordance with that analogy.

If progressives, or “casuists”, (or whatever), don’t think “murder” or “holocaust” are the best analogies, they must either rise to their own challenge and present a more appropriate and compelling analogy, or accept that “murder” and holocaust” are the best analogies available and commit to the actions required by those analogies.  To do less is to make an idol out of their subjective discomfort and use their feelings, not only as an excuse to do little or nothing about the injustice they are failing to describe, but to denigrate the motives and efforts of those whose actions are dictated by the best analogy that is currently available, not just to social conservatives, but to everyone.

Why do we need an analogy in this case?  Why stretch the facts to "approximate" the reality -- why not just describe the reality?  Aren't the facts of legalized abortion enough to make the case, standing alone?  If not, why not?  I find Justice Kennedy's dissent in Stenberg to be powerful and persuasive, and no analogy was needed.  Abortion is wrong, but it's not the Holocaust or slavery or the Spanish civil war.  Why do we need to pretend that it is?