He says this:
Economically conservative social liberals are the “jackalopes of American politics,” in the words of the National Review Institute’s Kate O’Beirne. The press keeps telling us they exist out there in huge numbers, but when you go looking for them, they refuse to emerge from the bushes.
In fairness, many people do describe themselves this way. Most of the time we simply call them “Democrats.”
But, in parsing conservatism, he royally confuses the term 'socially liberal':
One objection is that “economic conservatism” and “fiscal conservatism” are different things. One can be socially liberal and fiscally conservative, in the sense that you’re only willing to constrain your statist do-goodery to the extent you’re able to pay for it. This is certainly an intellectually defensible position.
"Socially liberal" doesn't mean supporting entitlement programs. It's not necessarily about statist do-goodersism. I think, to a good number of people, it means applying the same fundamental libertarian/classical liberal hands-off concepts underlying economic conservatism in the market context to the social setting. It's not a support of positive government actions in social affairs (e.g. entitlements), but less government intervention overall. It's about faith in individuals to make social choices and self-reliance, not about funding government choices in social affairs.
It means not caring about certain issues and barring government meddling in legal topics like homosexuality, marijuana use, or abortion, for example. Pulling back from government regulation in those areas is not going to cost the government more. Perhaps Jonah would like to call such stances "social conservatism." But that term clearly connotes the opposite in the present - namely, opposition to same-sex marriage, drug use, and abortion.
The type of things he seems to despise are the positions and outcomes of big government social liberalism. I think he can't find many jackalopes because he doesn't know what he's looking for - there aren't many people who are economically conservative that nonetheless support his conception of social liberalism.