It's all about how ideas spread, and how gullible, stupid, and/or ignorant people are. On the net, as I mentioned elsewhere here, you might be able to persuade one person that there isn't a conspiracy (unlikely though, since they usually believe them regardless of evidence) but you can't shut down the conspiracy websites (like Hoagland's one for example) that are the root of those ideas, which means that those ideas are still there contaminating the minds of people who are open to them.