Because of the initial chicken-and-egg problem. The Slashdot moderation system requires a large base of committed users willing to spend time on moderation, but if new users are only exposed to an unmoderated comment system, it's hard to convince them (or at least, the worthwhile ones) to exert any effort on the system. Even on existing sites, you're faced with the problem that the undesirable users are more committed to the site than the desirable ones, and enabling user moderation will make that so much worse in the short term that it will choke off the long-term. By virtue of its age, Slashdot circumvented this: no real competition, no expectation of moderation at all initially, and novelty of the moderation system all served to build a large base of potential moderators at launch of moderation. Even then, it's hard to estimate what degree of the success was just luck.

Unfortunately, it's a bit more complicated than that. Esotericism is, at least historically, a common religious practice. Gnosticism, Mormonism, at least a few Buddhist sects, and arguably the Masonic tradition all spring to mind. All of these have the idea that there are truths which should not be made available to the uninitiated, as they are not prepared to receive them correctly.

So this is the complicated problem: there are no really good grounds for condemning Scientology as a religion. The problems arise, rather, from the Church of Scientology as an institution. Letting aside the heavy-handed tactics used to recruit new members and to protect the Church, the fees charged for initiation seem to shift the practice from esotericism to exploitation. It's worth pointing out that very few people have objections to the Free Zone, emphasizing that the primary objection to the Church of Scientology is fundamentally organizational, rather than religious per se.