The danger of critical infrastructure being attacked digitally is already far greater than the risk of say, a bomb attack. Weakening our digital defenses to spy on terrorists is like throwing your laptop in the pool because you're afraid someone might light it on fire.
This is not true. However, it is important to keep in mind that were it ever true it would be because of blatant negligence on the part of human actors.
It is neither obvious nor inevitable that a nuclear plant will ever be attacked digitally because a nuclear plant need not be networked - even internally.
It is neither obvious nor inevitable that a hydro dam will ever be attacked digitally because a hydro dam need not be networked - even internally.
With an open mind and some creativity this could be true even for things like air traffic control and the power grid. They don't need Internet access. They might not even need IP.
If any of these things are fragile to digital attacks it is because they were gratuitously made fragile.