Ok, I'm pretty infuriated because I have seen this bullshit a thousand times, so I'm going to be blunt: you are wrong. This "advice" completely ignores the reality of the situation that someone who is being bullied finds him or herself in.
Fish asked for people to stop saying shit about him all the time, because it had turned into a thing of its own rather than a response to something he says; a sport of "who can call him a shithead in the most colourful way." That is bullying, plain and simple - when it becomes disconnected from whatever provoked it in the first place and turns into a "fun" pastime for everyone except the person being bullied.
I want you to take a moment and think about what it actually meant when Fish did that: he essentially admits that he feels miserabe, that there's nothing he can do about it and he's at the mercy of those who treat him like shit. He's showing his place as an "omega" and looking for support form others, because that's what he needs the most at that moment. So what was the response? Well, turns out that we humans when faced with such a situation, in our infinite nobility, tend to decide to bully even more to show our domination. So what followed was the typical "well, if everyone is treating you like shit, you must have done something to deserve it" justification to kick Fish down even further. So instead of toning it down people start muckraking and looking for excuses to justify further bullying.
So a guy reaches out for support from others and gets kicked down even further. Aren't we nice people?
That's how this shit works, and it's the same mechanism as saying a woman is "asking for it" when being sexually assaulted or "must have done something to provoke him" when being abused by her spouse.
It's fucking bullshit, and that situation is not comparable to coming across a few assholes that you have to mentally fortify yourself against like you describe.
Fuck this "advice". That's just bystanders like you looking for an excuse to not intervene and shush their conscience.