Originally Posted by
orbitmic
Now, the rules become more transparent and whether people are in favour or against, make it clear what difference Schengen makes - If you fly within Schengen: (1) you do not need to show id unless the airline tells you they want you to for commercial reasons (but in which case they need to inform you clearly), (2) you do not need to reclear security when you have a connection if the terminal is equipped with a dedicated ex-Schengen transfer channel, which most large and medium sized airports within the area now have (3) conditions for passengers from/to non-Schengen countries do not change.
On security, this is NOT a Schengen issue, but an EU/EEA-wide one: if you boarded at an airport deemed safe, which includes, in principle (save particularly exceptions to be made where a problem exists in a given location), pretty much all commercial EU airports whether within Schengen or not, there is no requirement for re-clearing security.
The problem, however, is that relatively few airports have set up traffic routes to allow for passengers from non-Schengen EU/EEA airports to be segregated from other non-EEA passengers and therefore de facto force the former to go through security again. The same is true in reverse in, eg., LHR (and other UK airports) which forces non-domestic EU-originating passengers to go through security again even though they should not have to simply because there is no segregation between EU and other countries in passenger traffic routes at LHR.