HR fires everyone involved in coworker group chat after new hire leaks it, even sends threats to non-employees

What happens in the group chat stays in the group chat, right?

Group chats can be dangerous things. If you're under a certain age, you know this to be true. Group chats are the way that cliques do their bidding. It's a finite group of people, so by necessity, it's exclusionary. And they can get toxic pretty quickly. You think that nobody is watching you, but this isn't always the case. All it takes is one mole to blow the whole thing wide open. And then you might look back and regret the things you've said and done. This is why it's good to be careful with them, especially in a work context. 

Group chats can also be necessary tools for communication. It's how you form bonds, share information, and organize things all in a certain place. It's an incredibly common tool for social organizing, and we shouldn't have to worry about being scrutinized all the time. We're entitled to our privacy outside of work, and even at work. But that doesn't always happen. If you're communicating with coworkers, you have to assume that that information might not be private forever. All it takes is for one person to snitch, and it all comes tumbling down. The best policy is to never say anything that might offend someone. But that's literally impossible. Anything taken out of context could end up sounding totally different from how you meant it. And then you're stuck apologizing for something that you didn't mean.