I disagree. This is great for Slack. They already have a product that people love, and of course this will raise their profile immeasurably, as people hear about FB's play and look into the available options.
Additionally, Slack now has just about the best tagline in the world: 'We're not Facebook'.
1. You show up to work, and Facebook is now mandatory.
It's attached to your real name, and Facebook
helpfully connects your real profile to all your
co-workers.
2. You now have to delete ALL of your non-work contacts,
for fear of gossip contamination, and NEVER use
Facebook outside of work again.
3. Everyone who has Facebook at work, now needs something
to fill the gaping void of recreational social media.
4. A new upstart fills the void, and Facebook crumbles and
implodes.
