The first question is obviously; do we as a community on Lemmy even want to try and stop them from scraping our content here?
If no; well. ok then.
If yes; how?
I'm not sure if "preventing access" to unregistered users would really prevent this. Pretty sure google has enough money and manpower to figure out a way to make it their mission to get around "can only accessed by members" content.
I personnaly agree with you. If content is not supposed to be searchable, maybe don't post it online.
It is a different problem for writers, artists and possibly even journalists.
But I think it's a fair debate - unfortuantely one that was one (or the only?) reason the whole reddit API debacle startetd.
On the other hand maybe Lemmy should allow certain communities allow an "only for members" view?
The reddit API thing started because reddit thought they owned the content and could lock it behind a paywall for people who want training data.
But that fundamentally isn't the case, so that whole thing backfired.
If someone wants to own the content and restrict access, they have to distribute it on their own instead of using a public platform. Lemmy is the wrong tool for that.
Literally already posting to a public space everyone everywhere can access if they were so inclined. I don't see how scraping that same content would make any difference, unless it significantly impacted site stability.