Which is exactly what would happen. Put the infrastructure in place and get people to accept that the government will be regularly censoring the internet to protect "morality and virtue", and the bureaucracy will find a reason to expand and censor things not deemed politically correct. It is far better to leave the internet a chaotic, relatively free venue for people to see and read what they want, than to allow the government to get its hooks any further into it and start "regulating" online activity to prevent people from seeing porn.
Even if the discussion is about laws already in place, the problem is that once the bureaucracy is created where federal employees decide what is hardcore (illegal) and what is softcore (legal), the lines will be moved by future administrations and sessions of Congress.
And even then, how would the government really make that determination? Who is going to sit around and create the regulations that govern what specifically falls into which category of porn. Do we really want government bureaucrats doing this? Are we really going to go after, say, couples who like posting amatuer sex videos online at the countless sites they use for this sort of thing? Will we be monitoring things like 4chan, reddit, etc, to prevent individual anonymous users from posting porn photos. If citizens have a private website and wish to put pornographic pictures of themselves, will the government prosecute them? What about all the hundreds of thousands of websites based overseas? Will the federal bureaucrats be tasked with sitting around reviewing every potentially porn related site from around the globe to determine if they are "soft core" and tolerable, or "hard core" and obscene. Where does it end?
The idea we are going to "crackdown" on porn is silly. It isn't going to happen. Rick Santorum only makes himself look foolish when he yaks about things like this. Sure, there are many social conservatives (not small government conservatives mind you) who find this kind of talk appealing - but these are many of the same block of voters that cast ballots for people like Pat Robertson, and in the end those types of candidates have pretty much no chance to ever win a general election anyway.