Jumping ahead from the first post:

States are obligated to honor marriages performed in other states.

States aren't obligated to honor civil unions performed in other states.

States (judges) "perform" marriage just as churches do.

You need a marriage license even if you're getting married in a church. There are (at least) those two ways of tieing the knot--but you need the state's permission to do so.

Civil unions offer far less to a couple than marriage, and a lot of rights disappear when a partner dies.