I don't argue that "it's ultimately hopeless". I think, with effort, it's quite possible to create a pseudo-private safe space online.
I just think that the bulk of your benefit comes from vetting the intentions and judgement of your participants, and not from technological means like removing search.
If you're able to trust your participants, technological means can be like a simple fence/lock, keeping honest people honest, but don't otherwise add a ton of extra benefit.
If you're not able to trust your participants, removing search will help _some_, but it might not be enough.
If it was just "determined attacker can do a search, and use the results privately" it wouldn't be a big deal. But they can then spread the result to everyone else in the world in a way that almost negates the barriers.
The recording option is closer, but search can be done retroactively, which makes a huge difference.
- We shouldn't bother checking for characteristics of credit card fraud at transaction time, because a determined attacker might get a fraudulent card through.
- We shouldn't bother checking IDs at bars, because a determined attacker might get a fake ID through.
- We shouldn't bother trying to prevent email spam, because a determined attacker might get a spam message through.
- We shouldn't bother making laws against recording people without their consent, because a determined attacker might do so anyways.
Please construct a more plausible argument than "it's ultimately hopeless". I'm willing to consider alternatives, but I'm not willing to consider fatalism.