Nearly as bad as assuming that all users of Rust believe writing it in Rust magically makes everything safe... each to their own high horse an all.
Anyhow - would you rather have a non-Posix-C compliant OS (i.e. remove strcpy()) or call out to an existing implementation because no improvement can be made when writing it in the language the rest of the library is being written in.
You could always RTFM, relibc is being written as part of redox-os because newlib wasn't doing it for them and there are probably safety improvements which could be made in some places.