The argument that government sanctions marriage purely because of the fact that it is the union that produces future citizen’s is a pretty good one.
The argument that state’s if so “childless’ couples should be illegal is pretty weak intellectually.
As Jews we are all aware of some basic concepts 1) Every rule has an exception 2) We rule based on the overwhelming majority, and regarding the other’s “Lo Plug” we do not differentiate.
The overwhelming majority of traditional marriages are with he intent of producing children, if not immediately eventually. The fact that there are exceptions is irrelevant. “Lo Plug”.