Francis Eugene George is not just a cardinal. He is also president of the United States conference of catholic bishops and sets the tone and direction for church policy and position in the country. His comments, therefore, on the positive attributes of the Church of Jesus Christ of Latter-day Saints (LDS), more commonly known as Mormons, seem surprising given the enormous theological and demographic differences between the two groups. Or do his words herald a spirit of co-operation among disparate religious movements in the fight against secularism?

Last Tuesday, in a speech called Catholics and Latter-day Saints: partners in the defence of religious freedom, he told an audience that Catholics and Mormons must stand together as a "vital bulwark" against those who wanted to "reduce religion to a purely private reality". The LDS church has proved its mettle in contentious areas. Were it not for their involvement in Proposition 8, there is every chance the same-sex marriage ban in California would not have been passed. Noting their ability to mobilise member support around issues that also concern Catholics, Cardinal George praised Mormons for their work to protect the rights of those who did not want to participate in abortion or assisted suicide and to defend marriage as a heterosexual institution. "When the government fails to protect the consciences of its citizens, it falls to religious bodies to defend them," he said. He also claimed that Catholics and Mormons shared more than a common understanding of religious freedom: they enjoyed a common experience of growing from a small, sometimes persecuted, religious minority to larger communities of 67 million Catholics and about six million Mormons.

But it's disingenuous of George to play up the similarities. Catholicism has been part of the US landscape for a lot longer than the LDS church. Immigrant communities ensure that the religion, its values and institutions, survive and evolve. It is the majority Christian movement in the US, boasting a profile and privilege that other denominations do not. And then there's the church's 2007 statement, which reasserted the universal primacy of Roman Catholicism.

So why the cosying up? There is an increasingly secular mood in the US and religious groups are all too aware of it. The Roman Catholic hierarchy knows it cannot rely solely on its congregations to campaign on touchstone issues and a "vital bulwark" – in the shape of the devout, wealthy and organised LDS church – is just what's needed to help it.