From what I've gathered the stop-start is really tough on the engines, and at the very least requiring way more frequent oil changes than the recommended intervals in order to make the engine survive.
If so, I'm not sure how much the environment is saved in the end.
I've heard it watching people tear down broken low-milage engines, and there's articles like this[1].
However, always good to question what you know. After some digging I found this very informative video[2] with Lake Speed Jr as a guest, which showed a vehicle benefiting from the stop-start technology. The key finding was that it reduced the amount of fuel contamination in the oil. Lake Speed Jr said he had found fuel contamination to be the most reliable indicator for oil lifetime.
Perhaps a confounder is that stop-start does seem to require more from the oil[3], so if the user has gone with a cheap oil that doesn't have the necessary additive package, then that might indeed hurt the engine using stop-start.
If so, I'm not sure how much the environment is saved in the end.