YOU ARE NOT CONTAGIOUS UNTIL YOU HAVE SYMPTOMS. And the first symptom is a fever, and that is what all of these people are self testing for. Everything else that is being done is being done out of precautions or over-reactions. So lets go through the things you just talked about.
The person on the cruise did not have Ebola, she didn't have a fever and she didn't have direct contact with the Dallas patient. She was a lab technician, who tested blood samples, that was the extent of her contact. Everything else was an over-reaction, by the her and everyone else.
The NY doctor called the CDC as soon as he had a fever of 100.3 and he is now being treated. The bowling alley cleaning was done because the bowling alley feared a negative reaction from the public, there was nothing that said he was contagious when he was there.
The reason for the Texas quarantine, was because 2 nurses got sick while he was there. So the initial thought was that there was hole in their procedures, none of the other nurses have tested positive since then.
Nothing would make them more trustworthy than being there and seeing what this virus can do. Everyone of these people has seen the worst effects of this virus, and they realize how dramatically their chance improve if they report the first symptom.
As I said before, 2 people have contracted the virus here in the U.S., none of them were innocent bystanders or family members of someone who was over there. If you are this scared of these people you should just walk around in a full bio suit all the time, it is the only way to be safe.