It's not just about bump and rebound. It's also about cornering and roll stiffness.
As you turn a corner the outside wheel loads up against the main spring and the unloading of the inside wheel is controlled by the rebound spring.
If you remove the rebound spring, there is nothing to control that unloading and that side of the car would just continue to lift until it runs out of space as the stub axle impacts the bottom crosshead bracket. This will give you no roll stiffness control and a horribly wallowy feel as you turn in.
If it's just a case of too short a rebound spring you will initially have very poor control of the roll stiffness until the inside jacks up a bit and then the stub axle contacts the short rebound spring to give you back a degree of very belated roll stiffness. Not as bad as no rebound spring but still a very wallowy turn in..
The solution is to use perfectly matched bump and rebound springs with the rebound spring just kissing the stub axle at rest.
As said before, read the Peter Ballard article and take time to assimilate it because it's not immediately obvious. Or at least it wasn't to me.
