Up to now, I always saw Slack as a tool for closed groups of people (for example, a company, a specific project, etc.). But suddenly realized that a lot of people was gathering around Slack communities, displacing the role of traditional forums. And wondered, how do you feel about it?
Building a community around Slack seems like a BIG NO-GO for me. To my understanding, content is non-indexable by search engines, and therefore it is not discoverable. Also, content is behind a paywall which is incredibly expensive (at 6.67U$/user/month), imagine if you have a small community of 100 people, we are already talking 8k/year. I am part of one such community that generates a lot of content, and some useful information falls behind the 10k messages limit. However, we can't afford the 15k/year we should pay to Slack.
On the other hand, self-hosting an instance of Discourse starts at around 5U$/month, and a managed solution is 1200k/year (with no user limit). I opted for a Discourse instance on Digital Ocean for the community I'm slowly building (mostly because I didn't even considered Slack at that time). Making it public helps with the indexing by Google, but I see that the interactions are different compared to how people behave on Slack.
I am happy with my decision for the time being, but wonder how are community builders, managers, and members, feeling about being on a Slack community, or a public forum, such as Discourse.