Hi,
Being someone who cannot be trusted i'd thought i'd add my bit.
As Sven Sixtoo said pratically all safety related procedures require double checking and this process applies also to the flight crew as well so to say they cant be trusted is not right in my opinion.
Some aircraft also operate with only one crew member per pair of doors so there is no one to cross check with so they gotta get trusted with that!
As for slides still deploying, yes it does happen but it has been proven through notes in the aircraft defects log that the slide was deployed mostly by pilots or ground engineers. Main reason for this is that they really only open the door from the outside. When the door is opened from the outside there is a mechanism which disarms the door should it still be in automatic and, we're all human, they forget this and open the door from the inside with the door armed.
(know there are some aircraft this dosen't apply too like the 737 which involves manually attaching the slide to the grit bar which can only be done from inside the aircraft)
Now for the door being opened with the jetty attached the slide wouldn't infalte. Reason behind this is that the slide needs to fall about six feet for the infaltion cord to be activated. A good example of this is the Air France or Britannia Airways crash where when the aircrafts left the runway all the landing gears collapsed redusing the height of the aircraft from the ground dramatically.
http://www.!!!!!!!!!!!!!!/open.file/565590/L/
As you can see from the photo the slides at door 1 and 4 are uninflated and on the ground. The slide at door 2 is inflated becuase as crew you are trained to pull the manual inflation cord incase the automatic inflation cord fails. Of course on the day you judge if you should do it depending on the crash situation and aircraft attitude and what will assist a speedy escape. So in terms of the slide at door 2 its inflated due to the crew member going into auto mode!
Cant find the pics of the Air France crash but the pic i mean is the one taken by a passagnger from the out side just in front of the nose as the fire breaks out. Think it was maybe taken on a mobile!
Hope this helps!
kempus