This, as David Kopel notes, is not an accurate summary of GOProud's position -- they support concealed carry laws so that gays and lesbians can protect themselves against rampant anti-gay violence. He suggests that the FRC should have instead made a slippery slope argument (that, regardless of intent, concealed carry reciprocity amendments would end up weakening state exclusion of foreign gay marriages), but adds the following:
obviously the FRC is free to organize is policy preferences any way it wants. Personally, though, I think that federal legislation which directly protects the Second Amendment rights of all Americans is far more important than whatever tiny effect the bill might have on gay marriage.
Well, Kopel might think that, but look at it from the FRC's point of view. Gay marriage will destroy democracy and is worse than child rape. Even an infinitesimal chance that such horrors might come to pass is far, far more important than any other legislation Congress might consider.