They may be against both in principle, but it's only gay sex that they find viscerally unpleasant and perceive as dangerous to society ("wha bout the chil'n?"). The religious justification is mostly an afterthought to bolster an already-formed opinion, which is why it is only applied selectively and they don't seem to care about the religious aspects of fornication, teen pregnancy, divorce, etc.
BTW, what ever happened with that "ban divorce" ballot initiative guy?