As same-sex “marriage” does when enshrined in law: A lesbian woman whose “marriage” has been legally recognized by the state applies for a position at a Catholic school. As is normal during the interview process, her “marital” status is undisclosed until she is hired and fills out the insurance paperwork. At this point, the school has been placed in the position of either following the state’s law and granting benefits to her partner, or following the teaching of the Church and dismissing her forthwith and facing the legal consequences of following their faith.
No laws restrict your community from performing whatever ceremonies they choose regarding two men, two women, a group of fifteen, or a dog and a toaster. The problem is when that recognition is forced upon those who do not share your belief.
Catholic children will be subjected to public schools telling them that two men or two women can be “married” - something directly at odds with the Faith. The state is directly telling them that their religion is wrong.
You stated that “no one religion” holds the truth as far as our country’s laws are concerned. I’m pointing out that it isn’t “one religion” but the common assumption of every culture everywhere. In declaring same-sex “marriage” to be legal, those states that have done so are embarking upon a sociological, psychological, and athropological experiment of unprecedented scale. 20,000 years of history, and this is the only area that every culture - pagan, Christian, animistic, pantheistic, atheistic, rational, primitive, even those isolated from all outside contact until discovery - has agreed upon. No other legal recognition - even murder - has been agreed upon like that. That’s an awful lot of data to handwave away as “not a valid argument”.