In the matter of the Cheney Family Feud: Something in me balks at leaping on the let’s-all-bash-Liz bandwagon.

Sure, it would be fun. For one thing, she’s wrong about same-sex marriage. As her sister, Mary, now famously posted on Facebook after her big sis re-proclaimed her opposition on “Fox News Sunday”: “Liz — this isn’t just an issue on which we disagree — you’re just wrong — and on the wrong side of history.”

For another, she isn’t simply wrong on substance. Her manner of disagreeing contains an element of smarmy condescension. “I love my sister and her family and have always tried to be compassionate towards them. I believe that is the Christian way to behave.”

Compassionate? We are compassionate to those less fortunate among us, the poor, the lame, the weak. We bestow alms, bind their wounds. That the Cheney parents weighed in with the same word — “Compassion is called for, even when there is disagreement about such a fundamental matter,” they said in a statement — is revealing about their lingering attitudes.

Mary Cheney and her family — her nuclear family, wife and children — don’t need compassion. They aren’t suffering from the affliction of lesbianism. They need decency and equal treatment under the law.

Could be an awkward Thanksgiving dinner (Ann Telnaes/The Washington Post)

Meanwhile, Liz Cheney’s invocation of religion is the icing on the condescension cake, with a subtext of voter pandering. It pained me to be around those poor fatherless children but I brought them presents because it was the Christian thing to do. What’s she going to do next — offer to wash her sister’s feet?

To me, the comparison between the right of gay and lesbian couples to wed and the long-settled issue of racial intermarriage is compelling. I agree with Mary Cheney: History is inexorably marching — actually, it’s sprinting — to marriage equality.

And yet I chafe at the notion that, at this point in the shortening arc, it is unacceptable to hold or express the contrary view. The issue of same-sex marriage deserves — for the good of society, it requires — a serious and respectful debate.

Where Liz Cheney has drawn her line is, after all, where President Obama was (or professed to be) not so long ago: no discrimination against same-sex couples, leave it to states, don’t amend the Constitution to define marriage for all time.

Then there is the unfortunate matter of waging this family war in public. It’s easy to imagine how infuriating it felt for Mary and her wife, Heather Poe, to be sitting at home watching Liz spout off on Fox News. The urge to fight back obviously was irresistible.

But taking matters further public? Going nuclear on Facebook? Heather’s post painted her sister-in-law as a political carpetbagger who shifted positions along with states:

“I can’t help but wonder how Liz would feel if, as she moved from state to state, she discovered that her family was protected in one but not the other,” Heather wrote in a post Mary shared.

And, “when Mary and I got married in 2012 — she [Liz] didn’t hesitate to tell us how happy she was for us. To have her now say she doesn’t support our right to marry is offensive to say the least.” But maybe Liz was merely being polite at the time. To say she’s happy for the married couple is not the same as saying she embraces their marriage.

Look, I would have been tempted to post, too. I would have been tempted to tweet. Then I would have thought better of it — or, more likely, my spouse would have told me to step away from the keyboard. That’s what Heather should have done for Mary. Instead, Mary reposted Heather’s incendiary message.

Social media knit us together but they also fuel our worst instincts. They serve as a powerful accelerant to the fire of anger. When we should be counting to 10, we are banging out 140 impulsive characters. In the hands of warring sisters, Facebook is a weapon of mass family destruction.

Finally, the implication that Liz’s position is one of political convenience is a bit rich coming from the wife of someone (Mary) who worked to reelect a president (George W. Bush) who urged rewriting the Constitution to ban same-sex marriage. After Bush’s comments in 2004, Mary considered quitting the campaign. She chose to stay silent. Not exactly a profile in political courage.

In her memoir, “Now It’s My Turn: A Daughter’s Chronicle of Political Life,” Mary described the Cheneys as the “most buttoned-down of families.”

If only.

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