then the ones driving “significantly” faster are the ones decreasing road safety. No-one is forcing them to perform “unsafe overtakings and such”.

I'm not claiming it is so, but I'm saying it's conceivable that if the autonomous vehicle drives slightly over the speed limit, with the flow of traffic, it may actually lead to a statistically significant drop in accidents compared to the scenario where it follows the speed limit. Yes, no one is forcing other drivers to behave in such a way, but they do, and because of that, people die. In this case, forcing self-driving cars to follow traffic rules to the letter would paradoxically mean you're choosing to kill and injure more people.

I don't think the answer to this kind of moral question is obvious. Traffic is such a complex system, and there are probably many other examples where the actually safer thing to do is not what you'd intuitively think.