Porn is regulated to some extent in publications. You can't buy magazines everywhere and not just anybody can buy them (legally).
The Internet is another matter as you pointed out. As an international conglomeration of computer networks, it should be next to impossible to regulate, short of having a world-encompassing government that could regulate and enforce regulations.
But the Internet is really just a global electronic version of conversation, which is the exchange of ideas and information by various means (the most common of which, for most people, is vocal). Internet porn can be regulated in the same way that we regulate our vocal conversations. Only say what you want to say and listen to what you wish to hear. If you are a parent and do not wish certain subjects to be heard or discussed among your children, then you must place barriers in the way of that happening. Most would agree, however, that parents can't completely shelter their children from "negative" influences, but must teach them morality as a check against exposure to such things. There are technologies available to help parents, and others, to bar certain types of Internet content from viewing. Kids though, as ever, will find ways around their parents' taboos if they are curious about the world and want to find out what they are missing.
Bottom line: we have to regulate Internet content ourselves to suit our tastes and moral viewpoints. We can't and, as far as I'm concerned, shouldn't, ban content.
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