Does anyone expect that to hold? It seems obvious that they just needed something that seemed vaguely like a legal basis to justify the decision. It's at least not as egregious as Griswald, but I definitely think they're reaching with the "feds can't have a custom marital definition". If they're going to say it's illegal for the federal government to define marriage because marriage is a state-level thing, they may as well also say it's illegal for the federal government to consider marital status altogether.

Well and beyond that, they're setting a strong precedent for future state's rights cases. I happen to be in favor of that by the way, despite ambivalence towards this particular issue.