I feel "just because Rust" leans a bit towards the overly-dismissive side. I'd imagine Linus isn't interested in potentially adding support for Rust "just because Rust" - presumably he thinks there are potential concrete upsides that Rust offers over C that are worth expending time and effort to investigate despite the potential complications from introducing a new language.
> In the long run it will cause fragmentation and increase complexity to such a point that it could destabilize the original project in its entirety.
This sounds scary and all, but I'm admittedly a bit skeptical about this argument. Why would introducing Rust support necessarily lead to the outcome you describe? Are there examples of such an outcome happening to other projects?
I guess it depends on what exactly you mean by "successfully". For example, while C is used for Linux and Linux is quite successful by most measures, that doesn't necessarily meant that there aren't areas where C isn't successful - in this case, a significant reason there's so much interest in Rust is precisely because there has not been success in producing reliably memory-safe code in C.
I think "forcing" might be a bit of a strong word for what's going on as well, but that's neither here nor there.