Yes, my argument is for running your own server. The matrix.org wouldn't be able to do anything to the gentoo.org server. If you choose to use the matrix.org homeserver, then the risks are identical to IRC.

You can also run your own IRC server. Risks are the same either way.

IRC networks are a closed federation. The servers have to trust each other and all servers of a network are usually administered by the same staff. Matrix is an open federation like email. The servers just speak the same protocol to each other and messages flow even if the server admins never have any interaction.

Matrix’s rooms are decentralised and we have decentralised access control to stop this from happening in the general case. Only a malicious server admin on your own server can hijack like this (or the one running a bridge in the case of a bridged room). And with P2P Matrix, every client gets its own server, so at that point hijacks will be entirely impossible.

I don't understand how that's possible. When clicking a matrix.to link, there is a room name and a homeserver hostname, right? How does that homeserver not have complete control over what information about the room is sent to the client?

Users/rooms on the gentoo.org server can interact just fine with users/rooms on the matrix.org server. That's basically the whole point of Matrix.

You may be suggesting that matrix.org could, for example, block access to the gentoo.org server (or a subset of its rooms). In that scenario users could choose a new homeserver (and not necessarily the same one) in order to regain access, instead of the entire channel having to migrate.

In the incredibly unlikely event where every homeserver on the internet is blocking gentoo.org, gentoo.org could simply allow user registration.

With IRC you are forced to trust the network operator with both your account and channel. Matrix gives you the option to trust someone else with both, neither, or either.

The room name + hostname is just one of potentially many aliases for a room that can be resolved by any server that has a member in the room

That's good to know! Thanks