What are some of the reasons for which mainstream non-Catholic Christians are against gender-neutral secular marriage?

What are some of the reasons for which mainstream non-Catholic Christians are against gender-neutral secular marriage? I get that some churches won't acknowledge **religious** gender-neutral or same-sex marriage (GNM) and why they won't support GNM, but why exactly does that extend to being outright **against** (as opposed to having no stand) **secular** GNM? Besides homophobia (like with the Westboro Baptist Church and the sort) and possibly the arguments here , what are there? In case the article is too long for you, here is a response that takes the article apart. I guess mainstream is: Orthodox (e.g. Eastern Orthodox, Greek Orthodox, Russian Orthodox, etc...) Roman Catholic Protestant (Lutheran, Baptist, Methodist, Episcopalian, etc...) Historic Non-Chalcedonian Churches (Coptic, Armenian, Ethiopian, Nestorian, etc..) Jehovah's Witness The Church of Jesus Christ of Latter Day Saints (Mormons) Seventh-Day Adventists