Ok, I'm going to explain this, one last time.

Can anyone who isn't against me and who can be neutral, jump in to tell me you understand what I'm saying when I explain this please.

Ok Duck:

At sea level, you fill a container with pressurised air and that's it. Fair enough right? No problems there, because the container is designed to hold that pressure.

Let's now take that same container into the sky as high as we can go...now tell me what would happen to it.

Why are you comparing a rocket which has 1 atmosphere in it with a pressurized container? Wouldn't it make more sense to compare the rocket to a container that hasn't been pressurized? Anyway...

I'll provide a little physics lesson here, free of charge of course.

So you take the container that wasn't initially pressurized into an environment of lower air pressure. The pressure within the container is now higher than that of the outside pressure, hence the forces on either end of the container's walls aren't balanced, with a greater force pushing from within the container.

If this container were a balloon, then it would expand to the point where the elastic is strained enough such that the inside pressure is creating an equal and opposite force to the outside pressure and elastic strain (the balloon applies a force inwards because the elastic is stretched and wants to go back to its unstretched state).

However, a metallic container applies the required force by its rigid structure. It's much like sitting on a chair. You exert a force downwards on it, and it exerts an equal and opposite force upwards on you (Newton's 3rd law), and as you apply more weight on the chair, the chair continues to change with it, until you reach the limits of its strength when it can't apply such a large force to keep you from forcing your way through and onto the ground.

Now, pressure is a measure of force / area. The surface area of the container doesn't change, so the pressure merely depends on the amount of air (number of molecules) and other variables such as temperature and volume of the container but we'll assume those are constant so we can ignore them. So 1 atmosphere of air in the container provides a pressure of 14.7 psi. That is, the inside walls are being pushed out with a force of 14.7 pounds (the pound is a mass and not a force but the Imperial system likes to be confusing like that, so I searched the value of the "pound" in psi to be 4.5 Newtons) on every square inch in the container. Any outside air pressure will exert a force back on the walls of the container. Let's say the outside air pressure is 1 psi, so every square inch on the container is being pushed inwards with a force of 1 "pound".

Since the container on any particular square inch is being pushed outwards with 14.7 "pounds" and being pushed inwards with 1 "pound" then the overall effect is an outward push of 13.7 "pounds". This isn't a very large force, but it's being applied over each square inch which is a relatively small area, so the pressure is definitely nothing to play with. Equivalently, if we filled up a tyre to 14.7+13.7 = 28.4 psi then the overall force applied to any square inch of the tyre will be 13.7 "pounds". It's exactly the same thing. This is how Newton's second law F=ma works. If you pull a rope one way with 1000 Newtons (screw the "pounds") and then pull the rope the other way with 1200 Newtons, then the overall effect is a 200 Newton force applied to the rope in the second direction. So if you took a rope and just applied a 200 Newton force in that second direction, the rope's acceleration in that direction will be equal to the first rope's acceleration.

So finally, what is the effect of taking a space ship into the vacuum of space in terms of air pressure? Well, the inside pressure is 14.7 psi, while the outside pressure is virtually 0, hence there is only one force to consider here and that is the outward force of 14.7 "pounds" on every square inch. Many containers can withstand such forces being applied to them, so it's not such a big deal.