Fluffy, as defined by the site's administrator, is someone who is shown to be ignorant (to the point of refuting knowledge) or are deluded into thinking things that break the laws of physics are real. The term itself, in this context, applies to "fluffy little bunnies"; people who think everything will go their way even if all logic points otherwise.
Beginners are the ones who are truly unlearned about things in a way that they don't have a firm grasp on what is real and what is not. While this is a stage for many in our spiritual lives (and it is naturally so; after realizing something previously thought unreal actually is real, many people are almost too open as to what else may be real. Media does help the cases of these people).
According to the definition above, true Fluffs are bad for the community as many new folk are susceptible to anyone who carries themselves as a knowledgeable person; this is why validation and cross referencing of sources are a good idea for everyone.
As for the folk who are truly mentally ill, to the point where they can't tell reality from fiction, they are not "bad" as they cannot control their perception. However, they have the potential to mislead just as much as the ignorant do.
The point of it all is that misinformation is bad. I hear a lot of cries to "Let them be! They aren't harming anyone" and that's not entirely true. For a person to claim they can grow wings or become a mermaid, they are leading gullible newbies to believe they can fly or stay underwater without consequence and that can be fatal. Most cases aren't as severe, but it proves the point I am trying to make.