"The reports of [Lopez's] death are greatly exaggerated"
Justice Scalia gets it:
[That Congress can regulate under the Commerce Clause activities that "substantially affect" interstate commerce] is misleading because, unlike the channels, instrumentalities, and agents of interstate commerce, activities that substantially affect interstate commerce are not themselves part of interstate commerce, and thus the power to regulate them cannot come from the Commerce Clause alone. Rather, as this Court has acknowledged since at least United States v. Coombs, 12 Pet. 72 (1838), Congress's regulatory authority over intrastate activities that are not themselves part of interstate commerce (including activities that have a substantial effect on interstate commerce) derives from the Necessary and Proper Clause. And the category of "activities that substantially affect interstate commerce," Lopez, supra, at 559, is incomplete because the authority to enact laws necessary and proper for the regulation of interstate commerce is not limited to laws governing intrastate activities that substantially affect interstate commerce. Where necessary to make a regulation of interstate commerce effective, Congress may regulate even those intrastate activities that do not themselves substantially affect interstate commerce.In other words, "The reports of [Lopez's] death are greatly exaggerated," and the attacks on Justice Scalia are, I think, also exaggerated. Justice Scalia is principled precisely because he knew that this case was a big deal for federalism, and that by joining the majority he would be undercutting the movement that he has had so much to do with.
It's a reason why Scalia would be a bad Chief (I agree), but not why he is unprincipled.
UPDATE: Orin Kerr points out that Scalia has voted a number of times in favor of the drug users, and that the "social conservative" claim isn't very accurate. He notes Kyllo and Booker, and I would add Employment Division v. Smith, which just a "social conservative" would not have written.