I might be an outlier in this thread, but I don't see anything wrong with them digging tunnels on their private property. It's no different than setting up a basement or wine cellar.
And given the unique history of their people, tunnels have kinda been a godsend to them to escape persecution so I see why they would be paranoid enough to install them.
My only concern is just the right-of-way and safety of the tunnels. For example, if the tunnels were to cross under the adjoining property owner's land or under public thoroughfare or public utilities, then this would be bad. Similarly, if there were no permits and safety inspections, that would also be bad because the tunnels might collapse or compromise the structural stability of the infrastructure at ground level.