> He trademarked it plain and simple and shouldn't be stripped of his trademark.
Not much about the law is 'plain and simple'.
Being granted a trademark isn't very good evidence that you should have been granted a trademark. Trademark offices don't do hours of exhaustive research into whether a mark has become customary, or whatever. They don't have the resources.
The idea is, if the trademark holder threatens someone with a trademark that shouldn't have been granted, the person being threatened will then do the research, and will apply to the trademark office to have the TM invalidated. They can then look at the application and decide. Shifts the effort from the trademark office to the parties. That's why trademark offices have process to apply to invalidate a trademark. Which /r/gaymers is using as intended.
Think of it like this: if /r/gaymers do prevail, then that means that, in the trademark office's opinion, they were wrong to have granted Vizzini the trademark in the first place. Which means that the "He trademarked it plain and simple" argument is meaningless: it's right if Vizzini ends up keeping his trademark, it's wrong if he ends up losing it.
And as others have pointed out: Being "stripped" of a trademark isn't a punishment. It doesn't stop you using it. It just stops you from using the law to stop other using it.
(N.B. IANAL, and in particular I'm only familiar with EU trademark law. I'd be surprised if US law was that different, but I don't know for sure, so the above may not be accurate for US law).