We can fly to Mars, but we can't install planet-sized plumbing?
You're trolling, right? Nobody is even proposing to fly to Mars any time soon. You aim yourself at mars and you coast for a long-ass time. Maybe by the time we have the tech to accelerate at 1G halfway to Mars and decelerate at 1G the other half the way to Mars, we'll have the tech to run a fiberoptic link through the mantle. But... probably not.