The issue with C is the silent issues like buffer overruns, i.e. even if you program defensively and with a proper security model you're still opening up to the possibility of leaking your missile codes by accident because you committed bad code
Personally I think bugs should be addressed, with better debug modes and tools. Take this example:
int i, array[10];
for(i = 0; i < 11; i++)
array[i] = 0;
Undefined behavior means that the compiler doesn't have to do anything, therefor it doesn't have to at run time test if the code is correct. It can assume that the programmer knows what they are doing. Thats why C has great performance, but also why bugs can be silent and hard to find.
But, It doesn't meant that the compiler has to ignore the issue. Its undefined behavior, so the compiler is free to do all the checks that a language that doesn't let you write outside an array do. Sure, then C will become just as slow as other languages, but you can now find and remove the silent bug.
This is why I think that debug mode, should be very different from release mode. The two compilers have entirely different design goals. Some compilers are starting to do this. Visual studio will for instance break if you access a lot of uninitialized values in debug mode, something that it will ignore in release mode.
There are loads of things that could be done to improve debugging that doesn't require the language to change or to slow down the release runtime.
I know what you're trying to say, because at least 95% of segmentation faults are easy to fix, but I take issue with this. The hardest bug that I've ever fixed was a segmentation fault!
You've obviously never experienced random crashes where the best idea anyone has is to bisect code changes in production and see when the crashes stop.
And you've obviously never experienced random crashes on customer machines where you've tested the crashing function for weeks, poured over crash dumps and ran the exact same function with the exact same data and could never reproduce it.
Buffer over runs, can be trickier, but I have plenty of tooling to find the issues.
Thread safety issues are what nightmares are made of.