I do not claim that porn is protected speech. I merely point out that Article I, section 8 does not give the federal government the authority to do anything about it. The authority of the federal government is limited to those matters specifically listed in the Constitution. If you paid any attention to the original understanding of the framers, you'd know that.
Insofar as viewing rights to pornography are for sale on the internet, the very nature of the internet makes such sales "commerce with foreign nations, and among the several states" and for that matter with wired "Indian tribes." Unless there were some way for an internet porn site whose administration was located in, say, New Jersey, to guarantee that only New Jersey residents would have access, such a site is engaged in international and interstate commerce. Furthermore, free internet porn sites are typically supported by advertising, largely by pay sites, and so are adjuncts to commerce.
As Justice Story points out in his Commentaries, Article 8 makes no statement whatsoever about the motive for which the regulation of commerce is put in the power of the United States. "A power to regulate commerce is not necessarily a power to advance its interests. It may in given cases suspend its operations and restrict its advancement and scope."