[tjwmason]

What are the legal incidents of marriage?

They are many and varied. They do inter alia include rights of inheritance.

Your problem seems to be that the proposed amendment prevents these incidents being required by the U.S. Constitution, or those of the several states.

Where does this prevent legislative action in any state (or indeed at federal level) granted these incidents?

Answer - it does not. It merely prevents activist judges from reading these incidents into constitutions. It says nothing about legislative acts (of the Congress, or of the states).

[goldstategop]

Which is exactly the point: to prevent judges from making doctrine in this area. It doesn't prevent the state legislatures or Congress from deciding whether to allow civil unions/domestic partnerships. That's all there is to FMA. Simple and straight.

[lugsoul]

Go back to con law class. The judiciary is not the only branch that interprets constitutions.

And the law would obviously prevent construction of state constitutions in various ways. For example, if a legislature purposefully drew a legal distinction that could not survive an equal protection challenge, the amendment would prevent any construction that allowed such a successful challenge.