"Fracking" for geothermal wells will supposedly not use toxic fluids. The reasons they're used for oil and gas extraction does not necessarily apply to geothermal wells.

There are some concerns about micro earthquakes and other disturbances if it's done near towns.

It seems like not using fracking, and just making several vertical lined bore holes might be better anyway though. In the best case you don't need any active pumps to drive the loop, so it can be much simpler.