If copyrights apply, only you and stack own the data. You can opt out but 99% of users don't. No users get any money. Google or Microsoft buys stack so only they can use the data. We only get subscription based AI, open source dies.
If copyrights don't apply, everyone owns the data. The users still don't get any money but they get free open source AI built off their work instead of closed source AI built off their work.
Having the website have copyright of the content in the context of AI training would be a fucking disaster.