I can't speak for the author - but there is some evidence that, to produce our power needs via wind/tidal means on a large scale (i.e. an appreciable portion of total production) would cause as of yet hard to predict ecological impact. You sap the energy out of your tide and wind and bad juju will happen to your environment.
"Hard to predict" is an understatement. For all we know, extracting energy from wind and waves could counter the recent perceived increase in hurricanes and tropical storms, or it could restore weather patterns to what they were prior to deforestation.
> For all we know, extracting energy from wind and waves could counter the recent perceived increase in hurricanes and tropical storms
The recent trend in hurricanes has been a decrease. (We can spot storms in places that we couldn't look before, but if we look just where we could look before, there's a decrease.)
