I think it is a retarded decision and I am opposed to sobriety checks and any other random stops of everyone. (Well, I suppose there are exceptions like checks for entering airplanes and whatever)
The justices rarely write 2 opinions for why they support or dissent on a particular ruling. Had I been a judge, and happened to agree with the ruling, I probably would have made an exception. Then people couldn't lump me in with the judge who wrote the opinion by saying that I thought the searches were "unconstitutional, but who cares, lol" if that wasn't my reasoning for supporting it.
But... whatever.