Worse than the work email spam at some of my previous jobs was the Slack spam - at least the email spam was work-related. Too many people substitute work for a social life and treat Slack like they’re on a group chat with friends.
There's nothing wrong with social chat on Slack. It just needs to be either in a thread or, better yet, in a dedicated social channel.
Saying people shouldn't have social chat on Slack is like people shouldn't have social chat in the office kitchen because it's part of the same office complex.