I agree it should be opt in but most platforms take ownership of your words as soon as they are submitted allowing the platform to decide if they want to sell the data for ai.

Lemmy.World does not (at least I didn’t see that in the TOS).

And besides, because of federation, its better if I explicitly state my claim to my content inside of the content itself.

_{Anti Commercial-AI license (CC BY-NC-SA 4.0)}