One person's "paranoia" is another person's "engineering redundancy."
If the designers of X Windows built cars, there would be no fewer than five steering wheels hidden about the cockpit, none of which followed the same principles – but you’d be able to shift gears with your car stereo. Useful feature that.
As security or firewall administrators, we've got basically the same concerns [as plumbers]: the size of the pipe, the contents of the pipe, making sure the correct traffic is in the correct pipes, and keeping the pipes from splitting and leaking all over the place. Of course, like plumbers, when the pipes do leak, we're the ones responsible for cleaning up the mess, and we're the ones who come up smelling awful.