I work as a gate agent for a major airline.
It's always a VERY VERY VERY VERY VERY hard call when having to "deny boarding" to someone. Fortunately I've yet to deny boarding to someone other than some drunk fool...
Needless to say I hope to never be faced with this situation.
I would think its impossible to blame or name all the individuals involved. That is because even when a cabin or flight crew member askes me for some help on a situation, if there is any reasonable doubt I call system ops control. Not only do they usually make the final call, they have no knowledge of what this person looks like, acted like, or anything. You tell them the facts and thats it. Period. I sorta keeps all parties safe. But then again I have no idea how US Awys. dealt with this.
Anyway, I could talk for days about being a gate/operations agent. So I won't ; )
In closing, I think if the general public knew how many flights have been diverted, delayed, etc. for suspicious people of !!!ALL!!! races, colors, religions, etc. these things wouldent be such a big deal.
Big deal: Miss the flight, talk to them, see whats going on, and accomadate them on the next flight.