There is a difference between pro-choice and pro-abortion. If pro-life means that no life is lost unnecessarily then pro-abortion would mean that all fetuses are aborted.
Also, if you're willing to let the entire U.S. go down in flames over this little issue, then you truly are no better than the Evangelicals which support Santorum.
By-the-way, those who wont support Johnson, because he is not as staunchly against wars as Dr. Paul, won't support him because wars cost an exorbitant amount of money; money we don't have, they don't not support Johnson just because people die in wars, it is a multitude of unidentified costs associated with war, which isn't the case with abortion.
If you want to compare a group of people who wouldn't support one candidate because he will end-up spending us into oblivion, to another group of people who wouldn't support a candidate because of a social issue -I suppose that is your right; however, it is a completely flawed comparison. Though, it does show where your priorities lay(a Federal Ban on Abortion which implies you don't mind using force to compel others to behave a certain way, as long as it is the way you want them to behave).
So, would you vote for a person whose personal view is that of pro-choice, but officially they want to leave it to the States to decide the issue?