I would fall back on the 10th amendment then:
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved for the States respectively, or to the people."
I can't speak for Ron Paul, but I suspect that he would argue that this "one size fits all" way that the Federal Government rules our lives, ruins it for everyone that doesn't agree with the law.
For instance, (I'm not equating alcohol to child porn but to merely the practical enforcement of such laws against them), shortly after the 18th amendment (prohibition) was repealed, SOME states STILL kept prohibition in effect, because it was a then a STATE issue, and if you didn't like beer or whiskey and didn't want to see it publicly consumed, you could move to Kansas where it was kept illegal until the 1950's (I'm going by memory).
Now, what if the Federal Government makes a stupid law, such as regulating what size your toilet tanks may be, even if there are no water shortages where you live? (I live right next to Lake Michigan, we have PLENTY of water). Well, too bad! Because, congress, in their infinite wisdom, have decreed that EVERY state must now sell 1.8 gallon toilets that you have to flush 5 times to clear it anyway.
I don't want to flog a dead horse discussing Constitutional law, (I'm not qualified), but I just wanted to convey that there is another point of view as to what role the Feds should be playing in regards to protecting citizens from common crimes.