How do you understand stall in terms of Newtonian mechanics (i.e. without Bernoulli's Principle)? Okay, so.  I understand how a wing generates life using Newtownian mechanics, to wit: the air molecules crash into wing, which is at an angle to the air molecules.  As a result, the air molecules are deflected downward and, by conservation of momentum, the wind must now have an upward component of momentum.
So why would it be that having too great of an angle of attack would cause stall?  I know the typical explanation is that the fluid flow over the top of the wing separates from the wing, but I fail to see how that would keep the air molecules crashing into the bottom of the wing from creating lift.
If y'all can forgive me a hokey MS Paint drawing:

 A: "the air molecules crash into wing, which is at an angle to the air molecules"
This only really happens when a plane comes in to land. After putting the flaps down, lift is greatly increased, but notice how the drag will greatly increase as well. This allows the plane to land at a safe airspeed, since it can maintain enough lift to come down gently while being at a much lower airspeed.
However, you can probably see that all this drag would be greatly inefficient during other phases of flight - if you look at photos of planes in cruise, you will notice how their wings are essentially level. While there are many factors that influence the amount of lift, including Bernoulli's principle, it appears that you are looking for something more easily understood with Newton's laws. One such factor is downwash - as air passes over the top of the wing, the Coandă effect ensures that the air jet follows the contour of the airfoil. Once the air reaches the trailing edge of the wing, it continues off the wing on that downward angle, which by Newton's third law means that the airplane will feel an  upwards lift force. When you stall, the airflow separates from the wing before reaching the trailing edge, so the effects of downwash vanish and you lose a valuable component of lift.
In every plane (as far as I know) putting in flaps steepens the trailing edge of the wing, which increases the effects of downwash while also introducing this "crashing" effect. As you can imagine, putting in flaps will decrease the stalling speed.
I'm a pilot, not a physicist, so perhaps someone could provide a more mathematical description or correct me if I'm wrong.
A: You cannot model fluid dynamics with a bunch of independent elastic collisions. If that's all there was to it, what you're saying would be correct and planes wouldn't experience stall at such a low angle of attack.
It's best seen with Navier-Stokes simulations, but you can always remember pressure is higher for lower velocity air. When AOA gets too high, it creates a larger split in air streams above and below the wing. This leads to a pocket of static, high pressure air above the wing that obviously applies some downward force.
You can also think intuitively as lift = total weight of air deflected down. With high AOA where the stream is split in two, the upper stream does not get deflected downward and instead flows over the high pressure above the wing.
A: The relevant forces are the weight of the aircraft and the vertical components of the forces on the wings. The sum of the latter forces must equalize the weight to keep the plane in the same altitude.
Following a naive idea, we could model the process as elastic collisions of molecules. They hit the wings horizontally and bounce at an angle of $2\alpha$ with the horizontal, where $\alpha$ is the angle of attack. Each molecule has initially zero vertical momentum and speed $v$. After collision, the vertical component of momentum is $p_v = mvsin(2\alpha)$.
The number of molecules hitting the wing per time is proportional to the vertical projection of the area: $n = kAsin(\alpha)$.
The vertical force is $$F_v = \frac{dp_v}{dt} = np_v = kAmvsin(2\alpha)sin(\alpha)$$
Making the derivative with respect to $\alpha$ equal to zero, we get the angle for maximum force of lift: $\approx 55^\circ$, which is of course completely wrong.
What is missing in my opinion is the tangential force. The viscosity of the air generates a tangential force in the direction of the wing, and much greater in the bottom part, due to the angle of attack. This force produces a torque that tends to rotate the aircraft. The fact that the stall is caracterized by the nose tilting downwards is in good agreement with this idea.
A: The way to think about is in term of the ratio of lift and drag.
Wing design is optimized for good lift/drag ratio. (Provided, of course, that the pilot maintains the optimal angle of attack for the wings and the speed of the aircraft.)
Aircrafts that are designed for aerial acrobatics have flat wings, giving the pilot freedom to fly the aircraft upside down, along a horizontal line.
The lift/drag ratio of acrobatics aircrafts is less good, but an acrobatics aircraft doesn't need to have distance capability.

So let's take the case of an aircraft that has completely flat wings. With a sufficiently strong engine that aircraft will fly. Here's the rub: with flat wings there is an optimal angle of attack too.
Stalling is that the lift/drag ratio becomes so bad that you keep losing speed.
To see that there must be an optimum: exaggerate the angle of attack to the point where the amount of drag exceeds the amount of lift. Clearly the aircraft will lose control at that point.
So: even when the wings are flat there is still an optimal angle of attack

Going back to optimized wings:
The purpose of the wing shape is to facilitate a good rejoining of the air that passes underneath and the air that flows over the wing. The better those two flows rejoin, the less turbulence. The less turbulence, the less drag.
The better the two flows rejoin, the better the mileage of the aircraft.
