They absolutely can, everything here is public. There are already people training models on nostr posts. Nobody here has expectations that they have control over the data they publish once it’s in the wild.
Discussion
So why is Slack treated differently?
When I use a paid service one of the things I assume I am getting in return is privacy and security. If that’s not the case then it should be made clear. It’s all about expectations and trust.
Slack is a product/service/platform.
Nostr is a protocol.
Completely different things.