Designers don't critize Comic Sans's usage when it's appropriate. It's when it's not. Like a funeral service's signage. Or a lawyer. And the massive amount of such objectively wrong usage in the wild is where you see designers crying about it.
However, I do agree that making fun of people picking the wrong font is a bit elitist. At least Comic Sans is easy to read, so one could do worse.
Of course comic sans specifically has turned into a bit of a meme so now you'll see all sorts of people complaining about it getting used anywhere, which is a lot sillier, but still not elitist I don't think.