Id's say "degenerate" is a catch-all for any activity which produces a supernormal stimulus, far in excess of what our Neolithic biology would be prepared for. Excess food, drugs, sexual novelty, and gambling all fall into this category.
You could certainly describe excess consumption of food, drugs, and/or sexual novelty as degenerate behavior. But GP appears to simply be referring to either consumption of or payment for pornography as a degenerate activity.