It is not Alito's adversity to congress using the commerce clause. Many people believe that congress has gone to far in its use (i.e. Lopez). But what really disturbs me about Alito's decision is that he expects Congress to justify its legislation to him before passing it. This goes almost to the level of reverse advisory opinions. The legislature would not craft laws that are black and white, but colored by all types of justification which would so confuse the application of law as to render it impotent.
And in passing both statutes, Congress made no
findings regarding the link between the intrastate activity
regulated by these laws and interstate commerce.
In addition, as I explain below, 18 U.S.C. section
922(o) might be sustainable in its current form if Congress made
findings that the purely intrastate possession of machine guns
has a substantial effect on interstate commerce or if Congress or
the Executive assembled empirical evidence documenting such a
First of all, no court has ever held that Congress needs to justify their legislation prior to it enactment. In fact, it has always been the exact opposite. Courts, due to the separation of powers, do not expect this to be done. Justification is expected if, and only if, the law is ever challenged in court.
Not only does this step over the line of separation of powers, it also places the judge in the spot of "intention" police. If you really want to see activist judges, follow Alito's lead.