How does ending Schengen prevent a fucktard that entered Europe as a fake refugee from driving a truck into a crowd of people? If you want to argue borders, argue European borders with the North Africa, but when you have people literally swimming across the sea to end up in some random beach in Europe, what the hell are we to do?
In this case even though they tried to deport him, Tunisia did not want to receive him. There is no good, clean solution to this fucking mess, but creating even higher inconvenience for regular European citizens by ending Schengen is not the answer.
I honestly don't see any clean solution to all this, there might not be one at all.
It wouldn't have stopped him getting into the external border, however Merkel welcomed ALL migrants who could get to Germany, noting Germany doesn't have ANY borders with non EU countries. However she basically opened the flood gates through that promise to all the countries like Greece and Italy.
That said, Schengen did enable him to get into Italy with no documentation, once he had done his attack in Germany. Hell, the thing I find the most scary, is that he was only caught due to a routine check on the Italian's part. Had he gone to other parts of Europe, he would probably have been able to disappear. :/
I'm not sure you can see it, but your own post is pretty much why such a stance is such a bad idea!