RE: But in the case of marriage, federal courts are forcing federal law/policy on the states, rather than leaving up to each state how to define marriage.
Also, there is NO FEDERAL LAW (not yet ) RECOGNIZING GAY MARRIAGE.
There is a “back door” federal law on homosexual marriage, in that the Supreme Court ruled that the federal government will recognize homosexual marriage from states where it is permitted.
The Defense of Marriage Act actually defined marriage in federal law, but, that definition was ruled unconstitutional by the Supreme Court.
So as of now, there actually is no federal definition of marriage, if you think about it.
The reciprocity clause causes all states to accept contracts formed in other states - Nothing more is needed. I have been saying this is the crux of the problem for years. The more comparable argument is in how one state does not have to accept the concealed carry right granted by another state - that is where the contrast lies.