Ahh where to start.
The 4th Amend only applies to the federal governmental employees. So the 4th Amendment does not apply to you and me as long as we are not governmental employees. So the airline personnel can search the bags as long as they do not do so if acting as an agent of the state; ie A person cannot be seen as participating in the search just to serve the purpose of the governmental agents.
Law has stated as far back as 1921 that private persons are seperate and distinct from searches conducted under state authority. An example of which is if a Fedex guy finds illegal contraband in a damage package he simply notifies the local PD and shows them the evidence. No laws have been broken as the evidence is gained from a private citizen who has not broken the law to obtain the evidence.
Also the 4th Amendment only applies to intracountry travel. As soon as you want to cross the US border the 4th Amend does not apply. They do not need probable cause to conduct a search of the person, vehicle, or propery. I won't even go into the exceptions to probable cause as this subject alone is an entire semester at some uni's.
As far a having stuff taken away just check the bag and be done with it.