That said... I'm not sure if it is enough since the others (besides Rudy) are pro-life in various degrees.
Hunter is the best of all worlds. The only thing holding him back is perception rather than any thing substantial. He's also the single candidate to recognize not only the immediate threat of Islamic extremism, but the long-term threat of Red China. The others seem to be whistling past the graveyard on that.
Rudy has three Achilles' heels (a pretty good trick for a biped)--abortion, immigration, and his personal life. But he did clean up New York, and sometimes gives terrific speeches.
None of the "top tier" candidates is ideal (Giuliani, Romney, Huckabee, McCain, or Thompson). Any of them would be preferable to letting the Clintons back in, but is any of them electable?
Thompson is probably the most promising of the five, if he can start to give an impression of someone who could actually win. (But Ann Coulter doesn't seem to like him.)
Part of the job of a candidate (and a President) is to change public perception, to change much of the electorate's view of him from "politician I heard about on the news" to "the guy who should lead the free world." If Hunter can't change the GOP base's perception enough to get him into the top tier, I don't see how he'll be an effective nominee.
The only think Huck has going for him is pro-life.
You say only and I say that is my number one issue. Sounds like a winner to me. However, he is not my first choice. Duncan is!!!!!!!!!!!!!!!!!!!!!!!!!