Frankly, the “civil unions” thing would be the least harmful. It has no religious implications and is just the state doing its thing about taxes, inheritances, etc. It’s a bureaucratic procedure that is meaningless except from a bureaucratic perspective.
The real problem is when they start calling it “marriage,” which enables them to trespass on religious territory.
The original suggestions for civil unions, btw, were simply households - that means it could be an elderly parent and an unmarried adult child, adult siblings living together, unmarried friends living together, etc. It didn’t have to be a gay couple, and there were advantages in this arrangement for the other non-gay people because it gave them tax breaks and certain automatic rights. The problem is that the gays took it over and made it some kind of sexual identity thing, but it shouldn’t be.
No; the least harmful thing would be to not legalize any type of homo unions.