Allies for a cause are allies for a cause. You’re being a fool. God uses who He will, to accomplish His will. Even sinners. You’re one too, you know.
2Jn 1:10-11 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: (11) For he that biddeth him God speed is partaker of his evil deeds.
We don’t need the LDS to preach the Gospel or stand against sins like homosexuality. I’d be careful to give any support to these people, especially when told that merely to wish such as these “God speed” makes you a partaker of their evil deeds. Considering how far Mormonism has come in this culture, even getting Billy Graham (or at least his son) to remove the LDS from their Cult section on their website, I think we can safely conclude that wishing them ‘God Speed’ has aided and abetted them very well.