Authorities should ban all persons without tickets from terminal buildings. In addition, there should be checkpoints on the roadway leading to the airport to verify identity or persons and what business they have at the airport.
Big failure in letting thousands to mill around the airport for no purpose other than cause disruption.
Sure, no picking up or taking your loved ones to the airport anymore, no spotting, no airport shopping, no hanging around at this damn cool and interesting place. You should realise that airports in many cases are much more than just the place to board a plane. They are shopping malls, business parks, intermodal transportation hubs & entertainment areas. Anyone still remembers the Dorian Gray club in the FRA basement?
The freedom of peaceful assembly and the freedom of speach (and thus the right to protest) are some of the most important Human rights. They are constitutional granted by all democracies and most of other countries.
FRAport (the company running FRA) tried several times to forbid demonstrations in the terminals and to expel protesters from the buildings. I hope I say this correctly in English: The Federal Constitutional Court of Germany ruled that freedom of assembly in public spaces is not restricted to public streets or squares, but all public places fulfilling similiar functions, which may include the public circulation spaces of shopping malls, stations or terminal buildings, even if they are on private property.
In the Frankfurt case this included the public circulation spaces in the checkin areas, arrivals halls and shopping areas. The area behind security is a different story of course.
The society and the individuals have to accept a certain degree of inconvenience caused by such lawful protests. E.g. you may have to accept the inconvenience to go slower or use a different route if your road is blocked by the sheer mass of protesters.
It is interesting how fast some people want to take away basic Human rights from others if their usage annoys them.