I wish the developer communities would realize that IRC has been around for years and performs much much better than Slack.
Both game engine examples but super helpful developer communities none the less.
The desktop app is unusably slow on my machine.
Then you'll see that there's also the question of "why IRC when we can just use Slack?" If you can't think of any answers to that, then you're not really equipped to eval the trade-offs.
(ok, i can think of one: "funny" emoticons. But i file that under hipsterism and if you really wanted, some IRC clients allows emoticons, but others might frown on your use of :sadbatman: :-P)
None of the positives for IRC that you mention facilitate the reason people actually use chat platforms: having conversations and forming communities.
Do you think people use IRC because it has an open protocol or because they want to chat?
The next step for you is to ask yourself what features Slack might have that does facilitate chat and community-building. Since you can only think of "funny faces", it sounds like you should actually download it and try it first.
And you'll soon be on your way to seeing other people as rational individuals with an appetite for different trade-offs than you instead of a bunch of idiots that just don't see the light.
> Do you think people use IRC because it has an open protocol or because they want to chat?
Most of the people who use IRC or Slack or Discord or HipChat or Skype or any other similar tech, do it because they want to chat. However not all uses are the same - creating a new chat room and entering the chat room are both uses, but the former means that you are in a position to decide what the people who will perform the latter will need to do. The people who will enter the chat room will not really be in a position to make much of a choice beyond entering the room/community or not, so their reasoning behind that choice is irrelevant when it comes to the selection of the technology for the chat room.
The people who will create the chat room, however, are those who will make those choices for everyone that follows in that room/community and it is to those people that i am referring to with "I do not think of any other reason to use something that for all practical uses is the same as IRC" - because there is really no reason to not use IRC and minor features that Slack or HipChat or Discord to some extent (Discord provides audio chat which some communities might prefer, although TBH personally i highly dislike it and any "server" - lol - i've seen that uses audio channels has them almost always empty) are not worth the restrictions these services impose on the other members of the community you are trying to create.