Social conservatives have lost the fight on gay marriage, even Rush Limbaugh observes. Regardless of the Supreme Court’s ruling, public opinion seems to have shifted irreversibly. How did it happen? Here are seven ways in which social conservatives fumbled the issue:

Anti-Prop. 8 protestors (Justin Sullivan / Getty Images)

1. They never explained how same-sex marriage “harms” heterosexual marriage.

2. They confused their own beliefs with those of mainstream Republicans, who were far less ideological and, in fact, were following the general societal shift.

3. They did not drum out of their ranks anti-gay (as opposed to pro-traditional marriage) voices, who portrayed the entire movement as intolerant and exclusionary.

4. They had no logical objection to states’ popular referendums in favor of gay marriage. With no imperial judiciary to rail against, they were reduced to making an anti-democratic argument that voters couldn’t or shouldn’t be allowed to define marriage as they saw fit.

5. They ignored the plight of heterosexual marriage (soaring divorce rate, rise in single-person households), which made their defense of “traditional” marriage seem insincere.

6. As more gay and lesbian Americans came out to friends, family and co-workers, the anti-gay-marriage voices were handicapped; they argued against an issue in the abstract while gay-marriage proponents could argue that Mike and Sam down the street or Sue and Ann at the office shouldn’t be denied the right to marry.

7. They insisted on federalizing the issue with the Defense of Marriage Act, leading to the current Supreme Court case and turning federalism (usually a conservative cause) into an argument about federal meddling into marriage.

This is not to say that if the social conservatives opposed to gay marriage had only been more deft in their reaction to pro-marriage advocates they could have won the issue. Once marriage became an expression of personal fulfillment (rather than economic necessity or religious edict) for most Americans, the issue was likely lost as soon as gay and lesbian couples showed themselves to be in committed relationships and desirous of the same security and legal rights heterosexual couples enjoy.

Nevertheless, it is instructive for conservatives defending other positions and advancing other causes that certain appeals work (e.g., fairness, inclusion) and certain ones don’t (e.g., appeals to historical norms, religious imperatives) in an increasingly diverse, secular society.

It also should remind conservatives (national security hawks, for example) that they cannot assume a set of assumptions will last forever (e.g., marriage has a distinct religious meaning, international threats are obvious).

Any political principle has to be advanced, taught and supported assiduously or it will cease to carry weight. Living in a political bubble of right-wing media, in which everyone agrees with certain nostrums (e.g. marriage is between one man and one woman, no tax increase is good, we need to spend more on national defense), leaves the right vulnerable to shifts in opinion and outmaneuvered when new, persuasive voices enter the fray. Conservatives should take the gay marriage issue as a warning — and not just on hot-button social issues.