Love the public policy result, hate the jurisprudence. We are now on the cusp of creating a national gay marriage law by judicial fiat (some Alabama gay couple will be filing a federal lawsuit against Alabama tomorrow as it were demanding state recognition of their marriage citing this case, and most probably win because same sex marriage are now a fundamental right), using the hammer of equal protection, which essentially gives the power to SCOTUS to pass any law at any time if it does not leash itself, because laws by their very essence treat folks differently depending on what category they fit into.
If Kennedy wanted to avoid going where he effectively did as described above, he would have just said that Congress cannot recognize gay marriages legal in a state for some purposes, while denying federal benefits on the other, and essentially demanded that the Feds respect state laws on this when it comes to using the marriage category for handing out benefits, using federalism arguments rather than the equal protection hammer (lousy public policy, but more restrained jurisprudence). Kennedy chose not to do so.
Having said all of that, and essentially wrung my hands, it is indeed hard to image beyond race and gender, just what is out there that is as intimate and fundamental as adult marriage, and the attendant horror show of Balkanized state laws from a practical standpoint, or a law as execrable as DOMA, so in that sense it is not as if SCOTUS's use of the equal protection hammer was done fecklessly, or will be particularly conducive as a precedent for SCOTUS to expand the scope of what its hammer hits and eviscerates in the future.
Translation - You're happy enough with the result.
