* I do think the cultural element may the the ur-source for the other differences. I say this because it is not just the pundit class who are less conformist. The British are less deferential to judges than we litigation-whipped Americans are. British are more cynical and dismissive of their politicians than we are, the US having too many secular cultists who cannot distinguish between the political and the religious. In the workplace too, British can be–or used to be–surprisingly candid and irreverent to their supervisors. They weren’t insubordinate, just extremely cheeky by US standards. Perhaps it was sort of safety valve for the class system? Since no one expected the class system to change, verbal fusillades from the inferior class harmlessly told the Establishment of their temperature without creating an obligation to do anything.
* In this country, the side switchers have tended to be people published in low circulation fora who had other income streams or could count on a ready stream of philanthropic funding (extended before or after switching sides). Right to left have included Garry Wills (academic posts), Edward Luttwak (in a way, and, again, academic posts), Michael Lind (misc. philanthropies), David Brock (sorosphere &c), and Damon Linker (whatever crumbs he gets). Left to right have included Irving Kristol (misc. philanthropies), Norman Podhoretz & family (American Jewish Committee), Seymour Martin Lipset (academic positions), James Q. Wilson (academic positions), Charles Murray (misc philanthropies), Richard John Neuhaus (misc. philanthropies, ministerial backstop), and Joseph Epstein (Phi Beta Kappa Society, academic post). Tacking one way and then another over the years have been Nathan Glazer, Robert W. Tucker, and Glenn Loury (f/t academics all).
* An American is his job, so it’s dangerous to be Mickey Kaus because you won’t get hired again by your former friends. The identification of job and status is not as extreme in UK. I remember Toby Young making this point about conformist Americans.
* Brits just like to argue. Debating is a national sport in Britain. Perhaps because their social life revolves around the local pub, where people gather to drink pints and talk for hours.
Another factor could be the great tolerance for individual quirks and excentricities, and for different opinions. Whereas conformity is a virtue in America, in England it’s perceived as a weakness and lack of character. There’s no greater sin than to be boring and conforming. Excentricity is feted and revered, unlike in America.
Of course, PC of late has greatly eroded UK’s freedom of speech and stifled debate.
* The British were a mono-culture until recently, with shared white ancestry. If you’re part of the in-group, you can say what you please among the other in-group members. They’re like your family, and you tolerate more obnoxiousness from your relatives than you would from a stranger. It’s only been recently that out-group members have appeared in Western cultures, and that certain cynical in-group people have been using them as a wedge to divide their own white group against itself.