Well you see, "fierce" is a word that means ferocious, as in it's just beastly how FAnatics can rock their fat and not give a shit about haters, and be aggressive about who they are (not a feature, since your brave FAnatic thinks that her overloaded stored energy are just so damn interesting that they just have to be part of her identity). So, you know, who cares about science, health, and all of that bullshit, because you can dismiss it with an attitude that would make the 90s seem lame, and that's immature empowering, and nothing that Tumblr can offer OBeasts that's more rewarding than desperate acceptance from a community of evolutionary failures being empowered.