You mention they are smart people. Do you mean there is a utilitarian motive to griefing, at least in the large scale cases? Effective trolling seems to efficiently polarize issues. When something is polarized it becomes much more discrete and easier to manage. That's why partisan politics do better than third options or bipartisanship.
That comment was aimed at a general purpose behind trolling. As for Kathy Sierra I don't know anything the issue, but I can make up something.
Say these people represent the status quo for tutorials. Sierra starts a whole new way of doing tutorials. What she does is also create a space for other new competitors to emerge, i.e. there are now a number of new ideas that can be combined in unique ways. This threatens to take even more market share from the original publishers. So, they polarize public opinion in regard to Sierra and her detractors. Now, no one looks at combining ideas from either party, just one or the other. Emerging market effectively eliminated. Additionally, the emerging market can no longer give momentum to Sierra's efforts. So, this indirectly damages Sierra's market too.
