> Compilers are not security sensitive, usually.

The compiler is one of the most significant trust boundaries we have. Its decisions can intentionally or unintentionally create vulnerabilities in programs compiled by the compiler, which means that if you can compromise a compiler you can compromise everything downstream.

Unsafe memory access in a compiler can be exploited in order to hijack the compiler itself (this is reported regularly in production compilers), allowing the attacker to then insert arbitrary code into compiled binaries. Not everything that a compiler absorbs from its environment is meant to be treated as source to be compiled, and in a memory unsafe compiler any of that input can silently turn into machine code in the compiled binary if an attacker is able to exploit the memory safety bug and hijack the compiler.

Of course they are, anything can be a gateway to inject backdoors, if security is not taken into account.

And as mentioned, if what Zig offers is already in Purify, there is hardly any added value over C and C++, without the headaches of a niche language.