> 27% of Swiss residents were born outside the country.
Swiss nationality is not linked to your birth country, it is linked to lineage. There are second, third, (fourth, fifth, sixth?) generation immigrants in Switzerland that are not Swiss. Conversly, there are Swiss nationals that have never set foot in Switzerland.
What events occurred that made the original Swiss people into Swiss people?
The point OP is making is that Switzerland undisputably has a very large proportion of immigrant population and that adding more should be carefully considered for various legitimate reasons, but it looks like you chose to be willfully ignorant.