Has been examined some more recently.
There have been many, myself included, who have described intense, dogmatic, self-defining belief as 'Romantic' in the classical, capital R sense. But one could well argue that this 'capital R' Romance actually differs very little from the more commonly used definition of romantic love. Certainly the prose of any authoritarian crank or aspiring martyr from any era is unfailingly grand, purple, and florid. It seems clear that to imagine ones own beliefs as the obvious truth that only the willingly evil object to does satisfy a sort of lust. To imagine ones own beliefs, customs, and folkways as the Only Path demanded of everyone seems to produce the same kind of transcendent rapture normally ascribed to the most idealized form of Eros. Ayn Rand would probably be the best and most famous example of this. As even her most horrific, genocidal putdowns of the leaching masses carry a definite air of satiation, purring agitation, and indulgence. (And then of course there's the rape fetish, which....)
Why this should be the case is for obvious reasons probably beyond rational understanding. I suppose it could serve as a substitute for immortality. To view one's own culture and belief system as the only legitimate ones can justify all the things one's self will never see or experience as not rightfully meant to be seen or experienced, aleve the smallness of one's own life with the illusion that, in the rightful course of things, ones own life will be eternally repeated by everyone.
Anyway, to get back to the old parlor question of why conservatives tend to report as more happy than liberals. Well there is, first of all, the fact that we are living in a prosperous country where happiness is the expected social norm, and conservatives are by their nature more likely to give the normatively expected answer out of hand without too much reflection. There is then again also the ecstacy of self-assurance that I described above. Brooks in the link article does point out that conservatives are joined by those on the far left in being happier than moderates or mainstream liberals. "One possibility is that extremists have the whole world figured out, and sorted into good guys and bad guys" Perhaps. Or it may be the case that the happiness of the True Believer is the same as that of the newlywed.