God knows how much electric 100,000 fast-charging stations pull. I doubt it's any more environmentally friendly than even 100,000 petrol cars.
Yes, supercharging is much worse for the environment than regular charging. The grids don't deliver enough juice for them at peak, and they have to store energy locally in battery buffers. That's another quite lossy conversion. And supercharging isn't as energy efficient in itself either - the heat loss is larger than with slower charging.
In countries that produce a good part of the electricity from coal and oil, that's not a good thing.