JOEL - I think that's what George Bush said to other world governments after the 9/11 attacks. One scripture comes to mind:

"He that is not with me is against me; and he that gathereth not with me scattereth broad. (Matt 12:30, See also 2 Ne. 10: 16 )

But Jesus is talking about Himself here. The other Christian religions of the world today are not against Jesus and therefore are not against us. In our opinion they may have a few false doctrines, but on the average they sincerely believe that they follow Christ's teachings as they understand it. In their hearts they are Christians and most conduct themselves accordingly and will recieve their place of glory in heaven.

An LDS Church Apostle once said:

"For the most part, our neighbors not of our faith are good, honorable people—every bit as good and honorable as we strive to be. They care about their families, just like we do. They want to make the world a better place, just like we do. They are kind and loving and generous and faithful, just like we seek to be. Nearly 25 years ago, the First Presidency declared: “Our message … is one of special love and concern for the eternal welfare of all men and women, regardless of religious belief, race, or nationality, knowing that we are truly brothers and sisters because we are sons and daughters of the same Eternal Father” (First Presidency statement, 15 Feb. 1978). (M. Russell Ballard, “Doctrine of Inclusion,” Ensign, Nov. 2001, 35)

Helping other faiths build churches is not helping the adversary. The "adversary" is not found in most religious organizations, but he can be found within any one person who lets him in, be they Baptist, Catholic, Jew, or Mormon.
We have been taught to love our neighbors and give Christ-like service to them. Helping another faith build a church is one way of expressing that love and promoting friendship and good will towards other religions and people. It can help open up their hearts and spirits to be more accepting of us in our communities. That was certainly the case in our neighborhood when one particular local Christian congregation needed help to rebuild a church that had burned down. They didn't ask us for help, but graciously accepted our offer to provide some materials and manual labor and together we helped restore the building. I think they even used our Stake Center for a few Sundays while their church was being built. They had no "agenda" against us and we had no "agenda" against them. Just neighbors helping neighbors. The concept works the same on a larger scale as well. Here is a link to one example you may have heard of:
http://www.acfnewsource.org/cgi-bin/printer.cgi?348