I've been banned twice, trust me I know what you mean. I have studied the ToS several times, and have come to the conclusion that anything not positive is literally bannable, at the sole discretion of the mod, in my opinion. At the very end the ToS includes:
Taking any other actions that are deemed inappropriate by Square Enix in our sole discretion.
In so many words, my interpretation of this line is, anything is bannable. What do you consider "inappropriate", and what does the next person consider equally "inappropriate"?
These are the lines of the ToS that I think can (and is) broadly interpreted, and leads to bans. Considering the context of my last ban for reference:
Posting that constitutes discrimination against another forum member or group (also including forming groups for the purpose of discrimination), insults, slander, libel, harassment of a group or individual.
You can be banned for simply making a claim against another user, it doesn't matter how severe said claim is. My suggestion is, to make sure you don't get misinterpreted, include "in my opinion", "I think".
Use of inappropriate or aggressive language.
You don't actually have to swear, aggressive can mean a lot of things, stay positive!
Posting aimed to create a negative impact on the community or its members.
How broad of an interpretation can you take for that you think?
Posting seeking to damage or disparage Square Enix, the forum, FINAL FANTASY XIV, or others.
Again, in other words, anything negative can apply here.
Posting content with the intention of criticizing either Square Enix staff or specific individuals.
MUST criticize only the idea.
And to finish this off, I assume this is what the otter posters were hit by:
Posting content that does not follow the theme of the category or thread.
Posting content that deviates from topics concerning FINAL FANTASY XIV.