Slack’s not great for resolving arguments.
I’m in one now at work. Nothing heated, just a disagreement about a certain design choice. But the ability to post short, sharp responses — not to mention the inherent satisfaction that would come from doing so — adds the possibility of making the whole situation descend to the point where it becomes just like a Twitter-storm. It takes effort to avoid that from happening. It took me effort to do so today.
Maybe something like an “argument” mode would help. When enabled, you can no longer make short posts and are force to write longer ones, maybe with a minimum character count of say 1000 or so. The post will also be delayed by about 15 minutes so that when you do slam a reply out, you have the opportunity to cool off, and reword it.