Each participant needs to verify each and every other participant. So for 2 participants that's 2 verifications. For 3 participants that is 9 verifications. For 4 it's 16. The square of the number of participants. With just 30 participants that works out to 900 verifications ... and who actually knows 30 people on the internet? Even if you could do the verification in a technical sense it wouldn't mean anything.
If you get a whole bunch of people together in real life for a meeting then chances are one or more of them is going to leak what happened. The problem is to a great extent inherent.