Of course it's fair. He built it to just have a person UNIX that he enjoys working on. Lots of other people did the same. Security was never a priority for them. Whereas, by that time, there were already multiple OS's with strong levels of built-in security. He could've copied stuff from them. There's even more now. They're still keeping broken model for (a) their priorities that put security low and (b) avoiding rewriting anything depending on broken security architecture. All the container developments are the classic solution to (b) but their security is often similarly shoddy vs what it could've been.
So, yeah, blame Linus and others in that ecosystem who do everything but make a solid foundation. Contrast that to OpenBSD for monolithic or GenodeOS for microkernel approaches where they bake security in at various levels. MINIX 3 for reliability levels they achieved 10x faster than monolithic UNIX's did. You get what you focus on. :)