Answer:
The readers themselves
Step-by-step explanation:
While I accept that contents providers could do more to prevent trolling, I personally don't think it lies in their hands at all.
People troll for a number of reasons, and most times, the quality of the content is not part of the reason.
They could troll because of the content provider themselves, because they have unresolved issues with them. Others troll because they're bored. Some people troll because they are simply bullies. At the end of the day, these sets of trolls, no matter how much the content provider tries hard, they would still troll nonetheless, making the efforts vain.
Succinctly put, the trolls are responsible for preventing trolling.