There was a disaster where the pressurisation switch was left in the wrong position by a maintenance crew [1], and the pilots didn't realise because they thought the alarm was for something else, and by the time they realised something was wrong they were starting to suffer from hypoxia and were no longer able to react properly. Additional warning indicator lights were added to the cockpit to make the situation much more obvious.
Now pilots would hear the warning, scan the indicators and see the indicator, and are trained to put on their oxygen masks immediately. The cabin masks would deploy automatically. Then they follow the checklist which is to descend to a safe level if the pressure is uncontrollable (which it wouldn't be if it's just switched off).
It's very unlikely the pilot would turn off cabin pressurisation, but it would be pretty gentle and warning alarms and indicators would start pretty quickly (including on EICAS on newer planes like the 777). The pilots could easily fix it well before their or the passengers' oxygen ran out.
I read a story about the "landing gear down" button being close and similar to the "shut off all engines" button in some bombers during WW2.
A few of them crashed after very long flights, on approach of the runway. Inexplicably, they suddenly felt right when they should have deployed landing gears.
So aircraft makers learned from that incident that no amount of training can mitigate a bad user interface. Especially if the user of your interface is dead tired after a 12h flight.
That was the "flaps down" switch, not "shut off engines". The key feature of fixed-wing aircraft is being able to glide unpowered; dropping the flaps however would be equivalent to yanking the yoke all the way forward.
But during a landing you would normally have the flaps down, this is exactly what they're for: to enable lower approach speeds and more visibility of the runway due to a nose down angle
After a few crashes that bad UX played a part in, I'm reasonably confident that in a modern aircraft that switch is somewhere hard to press accidentally.
(E.g., fuel selector switches that can enter an unexpected state while looking like they're in the correct state, take-off/go-around switches that could be triggered by a first officer wearing a watch reaching for the speed brake lever, attitude indicators with ambiguous backgrounds, three-pointer/drum-pointer/counter-pointer altimeters)
It's not going to be accidentally hit. And even if somehow it does get hit accidentally, there's a CABIN ALTITUDE warning that would go off before it becomes a problem.
Modern aircraft have very good warning systems that warn when configuration of the aircraft or systems necessary for life are in incorrect states, and the way they're used generally afford a decent chunk of time if something goes wrong.
