One-issue Voting?

Some people accuse those who vote pro-life as being one-issue voters. Of course, when a candidate doesn't support any intrinsic evils, a pro-lifer should consider a candidate's stance on all issues. But if a candidate supports an intrinsic evil, he disqualifies himself from consideration. I pose the following question:

If presidential candidate A said that he was in favor of killing, every day, 4,000 Americans over the age of 75, and if candidate B was against that killing and didn't have any other platform as heinous, wouldn't that one issue rightfully become the over-riding issue for many people? Would you call those who promoted candidate B "one-issue voters" as if that were a bad thing? Why should it be any different when it's 4,000 innocent unborn children who are killed in a day in the United States alone? (In the United States, since 1973, over 48 million human beings have been intentionally killed through abortion.)

Or if a candidate said that he supported terrorism, would you say, "I have to disagree with you on that issue, but what's your health care plan?"