a: Nebulous benefit, the community is fine, it's your website that isn't doing so well.
b: There are already programs similar to slack available that have less shitty business models.
c: You make a few assumptions here. 1: You assume users will not invite friends. 2: You assume people will completely ignore 'come chat with us on slack' at the top of every page.
What's ridiculous is that you continue to conflate 'the community' with 'the website, lewd.sx', in order to emotionally manipulate others into rolling over and accepting a substandard option. Despite it's problems, Slack is clearly superior to the lewd.sx forum in getting users engaged with the community.
Also:
""Slack has been stripped of all channels that could have a place on the forum, simply because Slack has leeched our activity considerably:""
You can't have it both ways, either chat/forum services are not comparable or they are.
If they are not comparable your statement above is fallacious, and if they are then clearly using Slack was superior to using lewd.sx
My whole problem with this is as follows:
I am on mobile a lot, chat is much easier on mobile than forums will ever be, regardless of design.
Poor planning capacity when making changes; this change should have been made at most 24 hours before completion of lewd.io, adding to a history of relatively poor planning (not that said history is big)
The less said about your motivation for doing this the better (as it definitely appears selfish at best)