What are some of the reasons for which Catholics are against gender-neutral secular marriage?

I get that Catholicism won't acknowledge **religious** gender-neutral or same-sex marriage (GNM) and why it won't support GNM, but why exactly does that extend to being outright **against** (as opposed to having no stand) **secular** GNM? Besides 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.