Yes you are. If you're willing to place all of America's national security into a scenario that is only computer generated (when all that could be halted by computer attacks), then you must certainly are gambling with America's survival.But we aren't doing that.
The current system was never designed to be secure, and it probably can't be made to secure. This was known from the very beginning, but it was overshadowed by the novelty and opportunity presented at the time the internet was made public.
The root of the problem that your solution can not fix is that by adding computers to the mix in the critical areas as we have, we have likely already made them too complicated to be controlled manually. You manual level will likely only give a signal to another computer controlled subsystem further down the line. Or that keeping a handle on what is going on in these very large system can be done manually either. The only reason they could grow to be this large is because we could depend upon computers to run them.
The critical areas you cite (in a 2021 composition of them) may be too complicated to be controlled manually, but the critical areas (electric, water, food, etc) as they were in 1960, are NOT too complicated to be controlled manually, because that is how that always were controlled. Get it ?
If you make everything run by computers, you will always totally be at the mercy (or lack thereof) of computers, and their vulnerabilites (which in future weeks/months/years) can never be fully or clearly ascertained.
Thus, a noncomputer element is needed in the equation to secure it.