[berkay]

Forget about whether IRC can do everything that Slack does. I can give you number of reasons (many already have in this thread and others) but it does not matter. Millions have decided that it is better for them. We can either decide they are all dumb or choose to throughly understand why they choose it.

I think that understanding why people prefer Slack over IRC is an excellent exercise for developers. I am highly doubtful that one can build software for non-developers without understanding this.