>So what if a person gives you the willies, and you say something to the crew, and it gives them the willies too?

Why should the crew act on willies when they have a huge security operation with its only function to thoroughly check people out for weapons that can cause harm to passengers?... Because they have to appear to take customer concerns seriously is the ONLY reason I can think of.
Anyone can concoct a story that causes their concern, and many are good at communicating the same too. But the crew has to be more objective and has to take into account things like the security done on all passengers and themselves. And the logical answer is to let the person worrying get off the plane.
Can you show any case where a person was asked to get off a plane because of a customer complaint and who later went on to hijack the next plane he got on? Or was arrested because he was a threat and it was later found that there was just cause?

FDR didn't say "We have nothing to fear but fear itself" for no reason. Our governments have done a bang-up job of instilling fear in all of us and of exploiting that fear to do little to improve our lives but look like they are doing important work.
When we let fear decide who can take a flight and who cannot we have gone way way too far.