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Unlimited Clean Energy - solar power from space has great advantages of ground based solar power, for example it is 24/7 power with no daily or seasonal variations, for 99% of the time, unlike wind power and most other renewables which are intermittent and unpredictable.   No power storage is needed, and your power assets are always performing for you, unlike solar panels which are idle at night and in cloudy weather.  

Saving the planet and saving the environment is a primary motivator and big selling point of space solar power.   It would allow us to dramatically reduce the damage to the planet caused by current or projected energy systems.

It would even be better than terrestrial solar power, which has a much larger environmental footprint than SSP.

There would be some environmental impact, but it would be less than the alternatives, e.g. stripping the ocean floor for methane hydrates, or vast stockpiles of nuclear  waste, or vastly increased carbon footprint from coal/gas power plants.

Initial studies have concluded the SSP environmental burden would not be significant.    The most vulnerable region would be the Earth's stratosphere, where ozone depletion might be an issue.   The aviation industry currently has a many times larger environmental footprint in that respect.   Thousands of space launches per week is not really "zillions".   It is certainly many times the present traffic level, but consider that there are ten of thousands of aircraft flying through the stratosphere every day right now.    Each aircraft spends several hours per flight in the stratosphere, but each rocket would only spend a few minutes in the stratosphere.

The propellants for rockets would most likely be hydrogen and oxygen, so that exhaust products would be water, which is harmless, with zero carbon footprint (if we ignore the synthesis of the hydrogen or the liquefaction of the oxygen). If other propellants were to be used, more environmental impact would have to be considered.

Most of the rocket propellant would be expended above the stratosphere, in the mesosphere and ionosphere, where the volume is so huge that no detectable impact would occur.

The scale of global energy projects today is immense, many times larger than the space business.   The SSP project would simply be increasing the scale of space operations to the level of today's petroleum industry, with a much lower environmental footprint.

FYI, I grew up in the oil industry, my father was an oil pipeline engineer. Professionally I have worked in the space business.  I believe I have a fair perspective of the respective scales of each industry.

In the long term, the flight rate can be considerably reduced by building the satellites in space from material mined from the Moon.

And indeed, space elevators might become viable in the 100 year time frame.