1. It's a 0.3% reduction of the German CO2 emissions so that's not really a useful point.
2. Killing 100 people also reduces CO2 emissions, doesn't make it a good idea...
0.3% is not an insignificant amount. Find a few more things like this to do to reduce emissions and it will add up.
Indeed, especially given the negligible amount of time this will add to a given commute, i.e. the majority of people's regular trips. Unless you drive from Munich to Hamburg at these speeds, but then you're just being a jerk to everyone who has to still live on this planet and should really be looking at the 300km/h trains. (Yes, they don't run every time they're scheduled for, but if more people put more money into the system, the system can improve.)