My thesis is that in a full scale national debate, Santorum or Gingrich would be defeated in a manner Romney wouldn't (and there's a reasonable chance, now 40% per Nate Silver at fivethirtyeight.com, that Romney will win). And by manner, I don't just mean percentage: such a contest would give all of us a chance fully to expose an unvarnished hard-core recitation of Santorum's very ugly positions. Free of the code words that a Romney or a Bush uses, we would have the unusual opportunity to have a direct debate.
And unlike some at Daily Kos, I think we will win such a debate resoundingly in a way that will promote social justice. I am a member of PFLAG, so I have a very personal stake in issues affecting our LGBT community.
I'm old enough to have lived in California when Reagan was Governor - I thought he'd never make a President, etc.So I have experience in being careful about what I wish for. But I'm also old enough to remember Barry Goldwater's catastrophic defeat and how it happened.
Santorum is much more like Goldwater than Reagan; in other words, if Project Hilarity produces Santorum as nominee, all the better!
First, on policy: Santorum on most issues of importance to swing voters is pre-1950 right-wing. Everyone reading this knows a litany of his outrageous statements. Much more right-wing than Reagan. Even Goldwater had some progressive/liberatrian positions that helped him in the general election of which Santorum has none: Goldwater supported a woman's right to choose and was for legalization for all drugs. On issues important to women, Santorum today is more reactionary than Goldwater was in 1964. To measure the temperament of the man, we recall Barry Goldwater's clear support for gays in the military - there is nothing in Santorum's makeup that allows for any re-consideration of his hatreds and intolerance.
Second, on personality: Santorum may look relaxed in a sweater vest, but when he talks about rape as a 'blessing from God' in explaining his opposition to abortion in the case of rape or when he invokes the guillotine in talking about Obama, he has a dark dour streak that is unappealing. Reagan was famously positive in his outlook and rhetoric, and even Goldwater had some positive moments than I've not yet seen from Santorum.
Third, most intelligent Republicans have concluded that his nomination would be somewhere between a calamity and a catastrophe. Daily Kos readers know the list of major conservative thinkers who've written this. They are way beyond posturing: they are obviously doing everything they can to avoid Santorum or Gingrich as their nominee because they know what will happen if the right-wing agenda is openly espoused. They've done well with the dog-whistles and code words in national elections - Santorum doesn't cynically use hatred to manipulate voters, he hates very clearly. This differentiates him from successful Republicans (with possible exception of Gingrich) in the past.
Finally, there's the practical consideration of national polls: with considerable attacks on Romney from the Democratic Party, albeit indirect, and virtually no attention to Santorum (or Gingirch), Romney does slightly better against Obama than either of the other two Republicans. Imagine how much worse Santorum will do if faced with a full-force national campaign.
Note:An earlier version of this was posted as a comment.