C was designed way before security was a concern. If somebody exploited your program, you could just slap them because they'd be sitting at a terminal in the same room with you - no need for fancy ASLR or controlling how many characters you write to a buffer when physical violence was a viable option :)
This isn't even remotely true. Computer security was a concern and an area of study long before C/Unix showed up. Unix (and by extension C) descended directly from the Multics project, which from its start in 1964 made security a central priority. Kernighan and Ritche were important members of the Multics project. Further, the idea that everyone who used the computers of that era were "in the same room" is also patently absurd.
I like my fantasy about how things were back then better, thankyouverymuch. At least this way I can believe they didn't unleash the flood of pwnage on the world while knowing better.