My first point is a Jewish one. Marriage does not equal Kiddushin. It is a civil concept. Were it not a civil requirement for certain privileges, many Jews would simply not be involved in secular marriage.
Kiddushin is well defined. It is JEWISH marriage. On that front, there is no compromise and there can not be a change. The Torah is explicit. Those who find an opening can call it what they like, but it’s not KIDDUSHIN, and anyone who calls it Kiddushin belongs to the Reform movement and is not considered part of mainstream Judaism.
How should Jews then react to the Civil contract of Marriage? I look at these issues through the eyes of Halacha. The Halacha which is germane, is that of B’nei Noach. The reality is that we cannot be seen to be supporting something contrary to the Noachide laws. Those people, however, have free choice. When they live in a union, which they already do, without the civil contract, they are technically in breach, although one wonders whether Tinok Shenishba applies 🙂 I do not think the Jewish vote classifies as Mesayea Lidvar Aveyra or that this even applies because they already do it without the contract.
So, what would I say if asked? I would say that Judaism does not support same gender marriage contracts. Judaism doesn’t proselytise, and whilst we have our views we recognise that the non Judaic world are governed by the laws of that land. We adhere to the laws of the land, but our personal stance as a religion is that there should be no change. At the same time, we do not support making someone an outcast because of their proclivities. Those are personal matters. We also feel that should the civil concept be legalised, all groupings based on gender preference should dissipate as this only causes animosity.