What are the stock spring rates? 100-120lb/in? well, when you bottom out, that spring rate goes all the way up to infinity, (aka, it cannot compress anymore). This transition from 120lbs to infinity causes unpredictable and uncontrolable response. When you cannot compress anymore, it is possible the wheels opposite to the side bottomed out can lift off the ground and flip.
Another way to put it. When you go into a corner springs transfer lateral forces into compression. Stiffer springs take more force to create the same amount of compression, but so long as compression is allowed, you will have no problem maintaining traction at all 4 wheels. When you bottom out, there is no compression allowed. Therefore, if you bottom out in a hard corner, the only way to absorb the lateral force is by you actually going up on 2 wheels.
You cut your springs ---> you bottom out more ---> you end up on the news when your car flips on I-4.