The author makes the point that the slow-down of the day is non-linear, and then he uses a linear equation to estimate the time until the Earth is locked to the

The author makes the point that the slow-down of the day is non-linear, and then he uses a linear equation to estimate the time until the Earth is locked to the Moon! His doomsday scenario of total tidal locking would never occur -- as energy is removed from the rotation of the Earth, the maximum power level that can be extracted would decrease. Also, the cost-efficiency would also drop. There would be a point where the day is "merely" longer, the Earth is not yet tidally locked to the Moon, but extracting more tidal energy is no longer worth the trouble. The original point however is still valid. Even if the rotation was slowed to just 1/2 of what it is now, the Earth would have a 48-hour day and that would obviously cause absolute havoc with the environment.