Sigh. Aside from the fact this comment adds no value to the discussion, anyone can walk into Zurich airport and buy a ticket.

By this logic, many public transport centres such as train stations wouldn't be public spaces either (not unheard of for a train station to have a ticket barrier too). There are adverts in places other than the airport too!

This is not true, you can't buy a ticket without identification and you can't get past security unless you go through several other checks. Going into a public area like out on the street is not even similar at all. Airports are not public locations, they are much more similar to the interior walls of a private business than a public location, which doesn't require you to pay to enter and produce varying amounts of identification.