The alerts being sent to Slack are normally from one of those alert databases (such as Prometheus and AlertManager). Slack isn't the source of truth for them, just a notification channel.
If it were an alarm database, an operator would be able to 1. Acknowledge the alarm 2. Manually clear an alarm that was issued in error.
Without those mechanisms, alarm handling becomes really difficult for an ops team, because now all you have is either a string of emails or a chat log.