The main point is that a new main line would revolutionize local and regional transport as well. So even if you don't build a high speed one, you get a lot of b

The main point is that a new main line would revolutionize local and regional transport as well. So even if you don't build a high speed one, you get a lot of benefit. But once you are building new lines, might as well make it a high-speed line. And we also should consider longer distances. Sure if you are going from Bern to Zürich 5-10min difference isn't gone be that big of a deal (well arguably if you have millions of people doing it, it does start to matter at least a little). But even if you look at Genf-Zürich, a new main line could cut that time by 40%-50%, from almost 3h to more like 1.5h. But what if you want to go from Southern France to Stuttgart or Münich. From Marseille to Zürich. We have major population density in a straight line from Genf to St.Gallen. Having a modern high speed rail connection across that population just makes sense.