When I was a brand new captain on a 737 I believed unless it was the last resort I wouldn't evacuate because of the high chance of injuries. I got a positive bomb threat going to LAX one day with a brand new FO. The caller of the threat said it was set for 2500 ft on the descent. I called dispatch to see if Palmdale was above 2500 ft and while they were looking it up saw my cabin was at 100 ft so said I was going to continue into LAX since I was downwind already and had insufficient fuel for Reno. I said make sure the pushup stairs are available because the fwd airstairs are deferred as inop. They said ok. I landed and approaching the area to disembark passengers saw no pushup stairs so called ops and said where are they? They said we are working on it. I advised the FA's we were going to use all the slides with a full load of passengers. The chief asked why did you use the slides if nothing happened at 2500 ft? I said because bombs have non FAA approved altimeters and sometimes don't work unless you are patient and wait. Never heard any more but I felt sick knowing all those people were going down the slides for another false bomb threat.
Evacuating is a tough call sometimes. It is probably used more than necessary but I thought in my case if I had waited 20 minutes after parking for the stairs and it went off the FAA would fry me and I would be responsible for lost lives and injuries. It is a judgement call by the captain and I wouldn't second guess him if he went for getting the people out. Sim training usually has you call the tower and check for visual signs of fire before evacuating. Jet Blue probably did the same thing they did to pass their sim check.