But that state authority doesn't necessarily place any burden on the federal government UNLESS the federal government is willing to allow those states to include federal benefits among the same-sex marriage.
This is exactly why the federal government must define marriage. It was the impetus behind DOMA.
Yes, if the couple CHOOSES to move FROM a state that supports same-sex marriage to one that doesn't, they lose those federal benefits.
When you read the Constitution, it covers NONE of these issues and the Founding Fathers made the correct choice to leave this to the states. It is then up to the states to decide how these issues will be addressed within their borders. If DOMA is struck down, the states need to have the ability to negotiate disbursement of federal benefits as they apply to same-sex couples.
This issue is no different than the marijuana one. Just because one state defies the federal government and agrees to let people openly purchase and use marijuana does not require another state to honor the same issue, even though they oppoose the use of marijuana.
This whole issue is about choices. Same-sex couples choose to create their lives together, just as heterosexual couples do. If that same same-sex couple chooses to relocate to a state that does not support same-sex marriage or same-sex access to benefits, that's a consequence of the choice they made to move.
We often hear, on FR, that choices have consequences and these issues that you are so passionate about are the consequences of the choices these people have made. If you believe otherwise, then you believe that the government exists to solve every issue that exists. And, some issues just end up sucking for those that don't fit within the mainstream.