"To sacrifice the greater good for the less and then not to get the lesser good after all–that is the surprising folly. . . Every preference of a small good to a great, or a partial good to a total good, involves the loss of the small or partial good for which the sacrifice was made. Apparently the world is made that way. If Esau really got his pottage in return for his birthright, then Esau was a lucky exception. You can’t get second things by putting them first; you can get second things only by putting first things first."
- From C.S. Lewis' 1942 essay "First and Second Things."
I think it's likely that any argument on the life issue is a result of differing views on what should be considered first things, and what should be considered second.