Wiki says: "A taboo is a vehement prohibition of an action based on the belief that such behavior is either too sacred or too accursed for ordinary individuals to undertake, under threat of supernatural punishment."
This clearly does not describe pornography, not even the Pope thinks this.
I'm not sure if you're a native English speaker or not, but the meaning of taboo extends farther than this. A simple definition would be something like "something prohibited to do/mention in respectable company"
This clearly does not describe pornography, not even the Pope thinks this.