Security vs liberties (and privacy)

No surprise that after all attacks by terrorists the cry for more surveillance, more intrusion into the privacy (of prospective terrorist, of course) is demanded. Gladio (stay behind) maybe already knew that...
There are several problems with this, I only want to reflect on one of them.
Some demands simply do not make sense or their sense is not spelled out. Some are exaggerated (simpler to ask for everything then setting clear limits). And these excesses discredit also the justified requirements for measures.
A lot of noise is made around free travel within the Schengen area and  passenger name records for flights. Should we add to this high-speed trains? Are really movements between countries in the Schengen zone the danger? Or just movement through rapid transport? To intercept all cars on the boarders would mean such a disturbance which may not justify itself.
Not quite independently, draconic measures are in demand after the attacks - and attacks are not so frequent. Thus, sometimes these measures become more lax, routine takes their edge by the time the next attack is being prepared.
On the other hand, think about the measures in airline security, the seemingly ridiculous limitation on liquids. Everybody could invent ways to circumvent them. However, since their introduction, no attack occurred on airplanes by circumventing them. By the way, the European Commission, feeling the ridicule, wanted to abolish them, but national security experts resisted.
Security measures prevented the attackers to enter the stadium in Paris and wreak much greater havoc then what they did.
These measures are inconvenient, but not a significant intrusion into our privacy. Significant intrusions are required with the argument that they help to track down prospective terrorists, to follow their movements and explore their plans. However, when two of the attackers of Paris were auditioned by Belgian police and left free, it is difficult to justify how more information or information on more people could have helped.
What is really missing, is not more data, but more analysis of these data, drawing conclusions and acting on these conclusions - and these conclusions are better to be sound as arresting innocent people on basis of data analysis would again discredit the whole exercise.