When people are sloppy with the language then some people try to divert. So if you talk about "marriage" or "same-sex marriage", they will often deflect to religious marriage. I tend to use "Civil Marriage" and "Same-sex Civil Marriage" (SSCM) in posts to ensure the basis is understood to be that which exists under civil law and not what a person's individual religious institution might think of Religious Marriage.
Look back over the last few pages, event the the OP Title is " Do you support legalizing gay marriage?", that which exists under civil law - plenty of post deflecting to what their religious views of marriage are.