Behind all the negative tone there is a valid concern though.
If you don’t know Rust, and you want to change internal interfaces on the C side, then you have a problem. If you only change the C code, the Rust code will no longer build.
This now brings an interesting challenge to maintainers: How should they handle such merge requests? Should they accept breakage of the Rust code? If yes, who is then responsible for fixing it?
I personally would just decline such merge requests, but I can see how this might be perceived as a barrier - quite a big barrier if you add the learning cliff of Rust.