Pornography should not be banned, as there is nothing compelling people to look at pornographic materials if they do not wish to do so; and there is little evidence that pornography in general, under normal usage, fosters any social ills that cannot easily be remedied by a little education.
For any kind of speech to be banned, IMO, there ought to be considerable direct and clear evidence that the speech in question is quite harmful, likely to imminently produce life-threatening acts by those exposed to it, and that it is all utterly without redeeming artistic, social or cultural value. I do not believe such a case can even be made for most hate speech materials, let alone for pornography.