Feif Un:
Civil Unions have nothing to do with an action done, its a legal business dealing. I imagine many unrelated people will (and do) use it to get health insurance and/or get around inheritance taxes. The problem is saying the act is OK (as you point out), and that is done by allowing them to “marry” C”V.
The idea is similar to an “Adult Interdependent Relationship”, which allows any two adults to state they depend on each other (such as a parent & child), thereby creating a single emotional & economic unit. This relationship (as far as the state is concerned) is completely platonic and will include any example of the case (e.g. a single child taking care of a single parent at their home).