Before digging into the opinion, written by shooter Justice Scalia, it appears that Scalia was willing to “stick to his guns” and do without the votes of a couple liberals it would have taken to reach a larger majority. He probably made it only as liberal as needed to get the 5th swing vote (Kennedy). Keep in mind that whether a decision is split or unanimous has no bearing on its effect as law of the land.
I recall Nino actually saying that mammoth decisions “should be” by a 5-4 majority. He actually believes that.