The Bugbear of Christian Legislation

In a comment on a previous post, DarkSyd (DS), objects in general to motivating legislation based on religion. An example he cites is Same Sex Marriage (SSM). He writes:

And legislation which is restrictive as opposed to progressive should have a higher standard. It's tough call sometimes to separate out which is which, I agree. But for example legislation against gays, in all it's many forms of discrimination, really has no basis outside of religious prejudice.

There are three obvious problems with this line of reasoning:

1. As I have said before, and even Mr Volokh agrees, that as legislation is based on ethics, there is no way to restrict religious ethics from the public sphere. After all, secular ethics are also based on just as many (but different) strongly held articles of faith as religious ethics. Our Constitution allows for no discrimination between them.
2. The idea that SSM "has no basis outside of religious prejudice" is not true. Completely secular arguments against SSM can be made easily from the perspective of social engineering, i.e., strengthening the nuclear family.
3. And finally, I think this is part and parcel with the secular fears of Christian's in government, which by and large I think are groundless. What is generally missing is exactly what the secular folks are afraid of? What legislation do they fear? By and large, the secular citizens support SSM and abortion which is opposed by the Christians. But that legislation all has secular supporters (and arguments) as well. If that is the whole of the fear, then it is all too much noise about a bump in the night.

I'll make one final remark. Mr Syd's comment about "different standards" for restrictive as opposed to progressive legislation echoes some of Mr Pierce's comments about proscriptive vs prescriptive legislation.