There are so many examples of teams successfully communicating state, sentiment and other information among each other with memes and videos an what not.
Also, to help people blow off steam. We don't need to be absolute productive units operating at 100% all the time.
Goofin off is healthy
The internet is such a large collection of knowledge, I just wish more people used it to improve themselves, or at least their understanding of the many different things we have in the world.
I tend towards being an introvert, and I'm not always good at coming up with an argument on the spot. I recognize this, and I will often end the real-time discussion by literally just saying "Ok, I need to go think about this before we discuss it anymore. Let's come back in a day or two." Just like you don't have to respond to e-mails the instant they come in, you don't have to do it for real-time or chat, either.
I will also do the same to others when I can. For example, yesterday I suggested a new approach to how a certain part of our product works, and pitched it to the team. There was only minor feedback so I just said "okay, go think about it, and I'll bring it up again later", so I will probably ask tomorrow to see if anyone has further thoughts on it. It's amazing what sleeping on ideas can do.
The thing I'm really trying to get at here is real-time doesn't mean "now! now! now!". There's absolutely nothing wrong with several meetings over the course of days or weeks or months. For strategic and key design discussions, there should absolutely be documentation written between those discussions. In fact, that's basically the way I operate: discuss, document, give time for people to review, and then discuss again, repeating as much as needed.
There's people that are opposite and want the response "now!", and don't want to take time to think through problems -- but I would guess there's a large overlap with the type of people that come over to your desk / call you and say "I just sent you an e-mail, did you get it?" and then only read the first sentence or two of your reply anyway.
The reality is that email fails to serve the purpose for complex discussions that involve many people, especially when you're using a rubbish email system like outlook.
Another form, be it meetings, chat, forum, whatever is required for this... and to be fair, gmail and the like offer some form of searching and sorting nested threads...
...but your complaint is broadly the same as the argument against having meetings in general.
Certainly, it is an oppinion, but not helpful or realistic.
Slack is disruptive, but 'just use email' isn't the answer.
Seriously, go read the lkml archives sometime, and go tell the authors of one of the most important and high quality pieces of foundational software in the world that they would be better served with something like Slack.
Real-time discussion is great if you don't have to think about what you're going to say before you say it. Unfortunately, that places a very, very low upper limit on the level of depth and consideration that a discussion can reach. Some decisions are hard enough and some situations are nuanced enough that you need to take your time with them, enough that the additional cost of making all of that time strictly synchronous can grow exponentially.
It also excludes large categories of people, including introverts and non-native speakers. I've worked with a number of people who just flat out did not or could not participate in real-time face-to-face discussions, but who could express themselves masterfully via email.
Of course, the "faster! instant! now! now! now!" crowd don't even have the patience for slower, deeper, better-reasoned discussions, which is why they shy away from any form of communication that has any more depth than a tweet or a PowerPoint slide. Slack is great for these people because they don't even have to string words together to communicate, they can just click on a reaction emoji.
Sure, some things (operations, for instance) have genuine urgency to them, and I think real-time communication is essential for situations like that. But if you're doing work that will have an impact on the span of months, quarters, or years--either major strategic business decisions, design, or project development--you're better served by thinking deeper instead of thinking faster, and deep thought is exactly what the long-form written word was invented for.