You both are right, what is not scalable is not encrypting messages to all when there are multiple keys, what is not scalable is sharing this shared secret and

You both are right, what is not scalable is not encrypting messages to all when there are multiple keys, what is not scalable is sharing this shared secret and rotating it when members are added and removed frequently. This scalability issue is a non-problem imo: * I don't expect large group VCs, and I don't expect the member set to be updated frequently * For large group VCs, the threat model is much different and you can do broadcasting (use the same key) For group chat I would say that confidentiality goes out of the window when you start having a large group, so having one key is just more simple to implement and makes sense.