So, everyone's talking about Saturday Night Live's God is a boob man video.

If you wince at the title, you're not alone – and watching the video will provoke one of two reactions. Either you'll be horrified at a tasteless and unjustifiable assault on Christian values, or you'll fall about laughing.

The video tells the story of Beth, a "small town baker without a care" who's asked to bake a wedding cake for a gay couple. It is "a story of liberal elites run wild"; Beth's Jewish lawyer wants her to say three simple words: "God is gay." "God is as straight as they come," is her agonised response. There are lines like "Christians are the most oppressed group in this country" ("Maybe," says a clearly unconvinced black woman) and "If God is gay, then why aren't there any gay priests?"

However, she needs an ally. In a state governor's office his staff are telling him about poverty, teen pregnancy and obesity. "We have to do something," they say. Enter Beth, who says in a tone of solemn conviction: "I want to deny basic goods and services to gay people." "Everybody out," says the governor: "this is the priority now." At the courtroom climax of the two-and-a-half-minute film she declares, "God is a boob man!" to a crowd of cheering supporters.

The film is an expert send-up of God's Not Dead 2, the film that plays to the narrative of Christian persecution which has become so entrenched among American conservatives. God is a boob man skewers state legislatures like Mississippi and North Carolina which have drawn national opproprium for their perceived anti-gay policies. It takes a pop at Kim Davis, the Kentucky court clerk who refused marriage licences for gay couples. It aims to make the preoccupation of conservative Christians with sex and sexuality look ridiculous, and because of its sure touch and comedic flair it succeeds brilliantly.

Full disclosure: I'm not a fan of the Gods' Not Dead franchise. I think the idea behind it – that, as SNL puts it, "Christians are the most persecuted group in this country" – is ridiculous. And while I don't enjoy seeing my faith mocked, I didn't find this skit offensive because it was mocking the God I don't believe in rather than the one that I do.

At the same time, I recognise that humour like this is powerful propaganda. Humour depends on the sudden recognition of truth in a situation that's incongruous or unexpected. When Beth interrupts the governor's crisis meeting to say she wants to deny goods and services to gay people, she's articulating and reinforcing what many people really believe: that Christians who pour their campaigning energies into this cause are driven by a rather hateful divisiveness. The underlying narrative of the skit is that Christians are irrational, that their ideas are weird, and that it's OK to make fun of them because they're funny without realising it. Obviously, no one needs to take their ideas seriously.

And there are three things to say about that. First, this kind of humorous take-down is capable of undoing, in two and a half minutes, hours and days of earnest work aimed at making the gospel credible to a new generation. American Christianity has some very bright individuals who are capable of rebutting any argument against the faith an atheist cares to put forward. Against the guerilla warfare of laughter, however, they're utterly helpless. That's not to say SNL's target is Christianity in general, it isn't – but to the extent that the dominant conservative evangelical model of Christianity stands for the faith as a whole, the image of Christianity takes a hit. Ridicule can succeed where Dawkins and Dennett have failed.

Second, God is a boob man is a self-inflicted wound. The moral panic over homosexuality has led conservative Christians into some very difficult places. Unnecessary but symbolic 'pastor protection bills', the Kim Davis saga, bakers and florists who don't want to serve gay customers – they all add to the sense that Christians are people who are determined to use any and all means to hold back a tide that's coming in anyway. And the rhetoric and the tactics of those who hold these views play well in their own groups, but they don't resonate at all well with those outside them. Hence the failure of Ted Cruz in New York. Hence God is a boob man.

Third, the skit makes it harder to have serious conversations about genuine issues. Yes, there are questions about the limits of religious freedom. Yes, there are questions about the power of the state and how far it should intrude into private life. In a purely American context, there are questions about states' rights versus federal overreach, and questions about the influence of lobby groups on the legislative process. But when there's a genuine – as opposed to confected – case of discrimination against Christians, the image that drops into people's heads is a spoof Christian baker saying, "Christians are the most oppressed group in this country", and it's a lot harder for that case to be heard.

So yes, it's funny. But it's worrying, too, because it shows how far out of the mainstream of public opinion conservative Christianity's fallen, and how far back it needs to climb if it's to be credible again.

Follow Mark Woods on Twitter: @RevMarkWoods