I know TSA looks for communications with extremists over Facebook or something. But why would they think they could identify suspicious activity in such a short

I know TSA looks for communications with extremists over Facebook or something. But why would they think they could identify suspicious activity in such a short time? They aren't professional or competent enough to join real law enforcement, why do they pretend to be intelligence officers? If someone wants to join a terrorist organization or something, and the FBI didn't identify them by the time they get to the airport, TSA ain't stopping them. So just let us pass in peace