On my recent flight to Ibiza, as I and the other passengers were boarding, there were many occasions where I could see right into the cockpit as the pilots and cabin crew were communicating back and forth for whatever pre-flight checks they were conducting. Being near the front of the queue at the gate, I was one of the first seated, the 10-20 minutes it took for the rest of the passengers to board was the time I refer to when I say I was able to see into the cockpit.
With it being my first flight in quite a few years, understandably I was extremely nervous. From the open cockpit to the smell of burning as the engines spooled up...
If we ignore terrorism, what is stopping a drunken passenger from, instead of turning right when they board at the front loading door, turn left and take a few steps into the cockpit, and if they were able to get into the cockpit, assuming they know absolutely nothing about the operation of a plane besides that pushing that pushing the throttles forward = more thrust = plane moves (faster), what damage could they do with a plane parked at a jetway or a plane parked out on the tarmac that requires a shuttle to drop passengers to the plane in order to board it.
If we introduce terrorism into the mix, what is stopping a group of strong men from forcing their way into the open cockpit past 1 or 2 cabin crew?