The “Write Correctly!” organization.

On the one hand, I agree with you, BUT in general, it's everyone's personal business whether to write to him with "mistakes" or not. For example, I don't always capitalize the first letter of a sentence... is that bad? o_O

No, it's not everyone's personal business.
At home, in a personal Word file, a person is free to write "cow," "banal," "Moscow," and generally anything they want, however they want. But on a forum, a person's post is their message, their address to other users, and forcing the person you're talking to to decipher their set of symbols is disrespectful.
It would be one thing if we were talking about classic "olban" or "preved" – but most "grammarians" are not even capable of adhering to these styles, confident that any illiteracy can be attributed to the peculiarities of the aforementioned "languages." We need to distinguish between the style of a language and simple illiteracy!
For those who consider such an initiative to be an infringement on a person's personal freedoms, I will cite a post by one of the forum users as an example.
"the game is actually very good. I liked that there is a teleporter in the Guild of Mercenaries to the dragons. There are: dragons, running dragons. And there is also a cave with djinns, ifrits, and encrypted notes on the walls.
and the class is cool".
This, citizens, is not a fragment of a post; this is the entire post. A short, concise, and elegant summary of M&M 6, which most of us love. I hope you enjoyed it.