As I wrote, I am neutral on the issue in civil matter.
From Thomas Aquinas:
“[Virtuous conduct] is not possible to one who has not a possible virtuous habit, as is possible to one who has. Thus the same is not possible to a child as to a full-grown man: for which reason the law for children is not the same as for adults, since many things are permitted to children, which in an adult are punished by law or at any rate are open to blame. In like manner many things are permissible to men not perfect in virtue, which would be intolerable in a virtuous man. Now human law is framed for a number of human beings, the majority of whom are not perfect in virtue. Wherefore human laws do not forbid all vices, from which the virtuous abstain, but only the more grievous vices, from which it is possible for the majority to abstain; and chiefly those that are to the hurt of others, without the prohibition of which human society could not be maintained: thus human law prohibits murder, theft and such like.”
and
“belongs to those sins chiefly whereby one’s neighbor is injured.”
Civil marriage of same sex harm no one except those in the marriage.
England, Randy. Free Is Beautiful: Why Catholics should be libertarian (p. 66). Unknown. Kindle Edition