Is the manufacture of biofuels actually carbon neutral?
What about the massive deforestation of Indonesia - caused by Germany's biofuel mandate?
The apparent purpose of this is pretty much a tech-demo for mars. In terms of minimizing environmental impact on earth it would pretty clearly be better just to send the solar energy to the grid and divert natural gas that would have gone to generating electricity to launching rockets.
We're not discussing "massive deforestation" here. Germany's biofuel mandate does not affect rockets in Texas.
Every rocket to Mars carries hydrocarbon that will never come back.