Let me see if I can simplify a fairly complex topic and the reason that I won't be using Matrix.
- Matrix collects a tonne of metadata. That data is not stored in logs where it can be easily deleted . It is stored in the database. These databases grow to huge sizes. One server with mere 15 users had a database of 70+GB and it was growing.
- The metadata collected is who left a message in what room, at what time, who saw the message, and the IPs of all concerned
- This metadata is synced across the whole Matrix federation.
Pardon my paranoia, but because I hold to some non-conformist religious and political beliefs I find this unacceptable. It won't be very hard at all to track what I may be doing on the Matrix network and who I am doing it with.
True, the messages themselves may (or may not (who really knows?)) be encrypted but too much information about the exchange is still being collected and replicated across the network. This is unacceptable to me. It puts me and my colleagues in danger.
It will only take one bad apple and things can go terribly wrong in a hurry.