Doing little nice things and having fun doesn't absolve any of the massive amount of bad that 4chan did. The KKK sometimes adopts highways and does little niceties for their members; they also killed more Americans than any other terrorist group in US history. Bill Cosby was America's father and a crowning icon of the Black community at the same time that he was a serial rapist. Jeffrey Jones was a funny actor before he got arrested for CP. DW Griffith and John Landis both made films that were vital to the evolution of the art form; the former revived the KKK, and the latter remorselessly murdered an old man and two children. (Full disclosure: I enjoyed
The Twilight Zone: The Movie before learning about what happened and even still love
An American Werewolf in London. I still think Landis deserved to be blacklisted and I don't care that we'll never see another film from him again.)
We could go on with this for a while, but the fact of the matter is that small contributions to society, and sometimes even big contributions, don't automatically forgive committing horrible acts. Doing nothing to atone for those acts, and going even further and committing even more of them, cancels out the good. And 4chan will never make up for what they've done, either because of the gravity of it or because they just aren't the type to do so.
Nobody cares if you, personally, were influenced or not. That's not even what is being argued. What matters is that numerous others were influenced to become hatemongers or become
worse hatemongers (that is, active assailants of the innocent). Propaganda is a problem because it works regardless of whether you think it does or not. The entire advertising industry is built on this fact. Coca-Cola doesn't spend multimillions on postering themselves like Mussolini because they think you're going to forget them; they spend it so that you'll subconsciously think of them as
the soda,
the drink you should buy if you are thirsty or at a restaurant. And they don't care if you, personally, don't buy Coca-Cola, because there's a shit-ton of people out there that it'll work perfectly fine on. And it works no different with bigotry.
I was on the internet nearly a decade before 4chan existed. You do not need to tell me about how it was. But back then, the garbage they produced was sequestered to a limited set of sites. Before 4chan, it was only on Rotten and other shock sites, and sometimes reposted at other small forums. And before that, it was just Stormfront and the like. But none of those were ever able to amass a following of the scale that 4chan did. None of them had the influence. None of them leaked their ideas out into the larger offline world and managed to ruin people's lives or end them. And they didn't influence normal sites to become the same or worse.
Criticism is not censorship. If someone has the right to say asshole things, others have the right to call them assholes.
That is real freedom of speech.
And let's make one thing clear that the 4chan crowd doesn't get until they get arrested:
nobody has a right to
absolute freedom of speech. Every single country on Earth has a legal concept called reasonable restrictions on speech. These are laws that stop speech or media that causes serious and obvious harm to others. That generally includes laws against death threats, CSAM, inciting a panic, inciting a riot, inciting an attack on the government, and inciting a lynch mob. (There are others, too, depending on the country.) So if they get arrested for that shit, they won't be "censored"; they will be arrested for a real crime with real consequences that nobody in their right mind will defend.
This is not stupidity. This is not "tReAsOn To HuMaNiTy."

This is being civilized. This is being
not a pedophile. This is being
not a murderer. This is living in the real world, not in a cesspool of idiotic psychopathic fantasy.