Sarah Huckabee Sanders is a tough cookie, as anyone who's watched her White House press briefings can attest. So when she was asked to leave the Red Hen restaurant in Lexington on the grounds that she was President Trump's press secretary, she didn't take it lying down.

Her tweet saying of the owner, Stephanie Wilkinson: 'Her actions say far more about her than about me. I always do my best to treat people, including those I disagree with, respectfully and will continue to do so' has 168,000 likes, 48,000 retweets and 156,000 comments.

Ah, but those comments, now. The likes and retweets might be marks of approval, but the comments – let's just say not so much. 

What's created headlines, though, is that these protests occurred in what is in some peculiar way a protected space. They transgress a sort of primeval code of hospitality. Eating together is our most basic form of social bonding. Breaking this charmed circle is not done. It is not just rude, we tend to feel, it is Wrong.

What was it that tipped the balance and made someone who described herself as 'not a huge fan of confrontation' take such a public stand?

The immediate trigger was the objection of Wilkinson's employees to Trump's ban on transgender people serving in the military and to Sanders' defence of the policy of separating parents and children at the Mexico border. When attorney-general Jeff Sessions defended it from the Bible, Sanders backed him up. Trump, having first lashed out at his critics, belatedly realised just how toxic the images of children in cages juxtaposed with Nazi concentration camp pictures were, and backed down.

But Sanders, thanks to her earlier comments, was inextricably associated with a policy regarded – surely rightly – by large numbers of people as downright wicked. So was Department of Homeland Security secretary Kirstjen Nielsen, who was heckled by protesters while dining at a Mexican restaurant in Washington DC.

This was not just a political difference over the technicalities of immigration enforcement. It was about right and wrong, good and evil. America is used to seeing itself as the good guy. Those pictures made that impossible.

There have been plenty of contrasts drawn between the indignation shown by conservatives about Sanders' and Nielsen's treatment and their enthusiastic support of the right of Christian bakers to decline service to gay customers preparing for their wedding. It's an apt enough parallel: in both cases the culprits were acting according to their consciences. What's sauce for the gay cake is sauce for the Red Hen.

But denying people the opportunity to eat together is on a different level. It's not just an abstract calculation about the limits of conscience. It's a visceral rejection of actions and attitudes people know, in their innermost being, are utterly unacceptable in a society that claims to have a moral compass. It's a refusal to be associated with wrongdoing, to compartmentalise and pretend life is normal when for migrants on the Mexican border it is sheer hell.

By tweeting her outrage at how she'd been treated, Sarah Sanders showed she didn't get that. And if the rest of the administration shares this blind spot, it may yet have political consequences.

It's not just America, though. After decades of consensus, Europe is once again in a period where politics is about morality. British rows about Brexit, intense and polarising as they are, are trivial compared to debates about what to do with migrants drifting at sea, who counts as a citizen, and whether the continent is Christian or not. Technical questions about how to manage problems have become complicated by moral questions about how to treat people.

And this is Christian ground. We don't have any more expertise on policy details than any other civic group, when it comes to migrants and borders. But we do have a highly developed sense of right and wrong, based on being attuned to the Fatherhood of God, 'from whom every family in heaven and on earth is named' (Ephesians 3:15).

We feel it, viscerally, when we see wrong being done. We have to call it out, even if it means looking rude. We have to call people to repentance and stand up for the vulnerable.

There are times when it's just not OK to differ.

Follow Mark Woods on Twitter: @RevMarkWoods