The United Methodist Church has rejected a request by a group promoting so-called "intelligent design" to have a display at its General Conference in Oregon in May.

The decision, reported by the Christian Post, appears to raise questions about the limits of tolerance in what is actually quite a tolerant denomination. More widely, it hints at a broader issue: when is an argument to be regarded as settled beyond the point at which it can be reopened?

From the UMC's point of view, it may not in fact be such a big deal. It's the first time the denomination has had "outside exhibitors" at its annual conference and it is entitled to be picky about whom it includes. It is on record as being opposed to creationism in general and sees intelligent design – of which more later – as a fig-leaf or stalking-horse for that.

Its spokeswoman Diane Degan told the Christian Post: "The Commission on the General Conference determined that the application by the Discovery Institute did not meet the guidelines established for exhibitors in that it was not consistent with the purpose of the exhibitor programme."

She said the programme stated that "exhibits are not to provide a platform to survey or test ideas but to provide products, services and resources which are credible and proven to help local church ministries, and, in their opinion, it conflicted with our social principles".

The vice-president of the Discovery Institute, which had asked for the display, is not happy. John West pointed out that the UMC's policy referred to its opposition to the introduction of "faith-based theories such as Creationism or Intelligent Design" into public schools, which he said was not the Discovery Institute's policy.

"I would point out that the UMC's slogan is 'open hearts, open minds, open doors,' and UMC leaders claim to be in favour of open dialogue," he said. "But banning us from even having an information table is not open-minded. It's close-minded in the extreme."

But what makes intelligent design so inimical to UMC values?

Its first use was in a book entitled Of Pandas and People, a 1989 textbook designed for high school biology classes. It was originally aimed at defending creationism, but after a ruling against the teaching of that theory by the Louisiana Supreme Court in 1987, references to creationism were changed to "intelligent design".

The movement is fundamentally a version of the teleological argument for the existence of God. While it encompasses a range of views about evolution, with some proponents saying God simply guided the process, others are keen to argue that some life-forms demonstrate an "irreducible complexity" that means they have to have been specially created by an intelligent directing force. It critiques evolutionary explanations of life, saying that they are inadequate accounts of origins. It usually avoids saying that the intelligent designer is God, but the implication is clear.

Because of its apparent attempt to bring untestable assertions into the scientific arena it is widely regarded as a pseudo-science whose assertions don't stand up to scrutiny. Scientists have been withering about it: the US National Academy of Sciences has said that "creationism, intelligent design, and other claims of supernatural intervention in the origin of life or of species are not science because they are not testable by the methods of science", while it has also been condemned by the US National Science Teachers Association and the American Association for the Advancement of Science.

But still: the Discovery Institute argues that people should be allowed to make up their own minds. Arguments based on freedom of speech are often strong ones. However, the UMC has taken the view – expressed though it is in dusty legalese – that in allowing the promotion of intelligent design at its conference would to connive at something which is, not to put too fine a point upon it, not true.

In this respect, it is surely right. It's always possible to find things about life and its development that evolutionary theory has not yet succeeded in explaining. To argue from this that the answer must be "God did it" is ultimately self-defeating. Science advances, the number of unknowns diminishes, and God is driven into a smaller and smaller space accordingly. This "God of the gaps" approach has long been discredited.

The UMC appears to have taken the view that giving a platform – no matter how small – to a view as mistaken as this undermines the credibility of the gospel because it encourages people to believe things that aren't true. Building a faith around falsehood is putting people's souls in peril.

The Discovery Institute may not like it, but the UMC is surely right to stand its ground.

Follow Mark Woods on Twitter: @RevMarkWoods