Where does the idea fail?
I don't know how the prof would answer. But irregardless of the math on the strength of the cable, the accounting in dollars will make it fail from the cost of removing every existing satelite in orbits below the cable counterweight altitude.
Not sure about the whole idea, but beaming the energy to the climber via a laser is a stroke of genius.
They could even catch the sunlight at the top of the platform and beam it downward to the climber.
I realize that it probably is just a tiny bit of energy, but wouldn't a long tether with 20,000 kg on the end slow down the rotation of the earth, perhaps a tiny bit. This would be like a skater putting their arms out while in a spin, to slow down the spin. of course, it would be so tiny, not even noticable.