A ball joint is a ball captured in a cup. The "capture" is pressing the rim of the cup over a portion of the ball northern hemisphere. Enough force applied in a wrong direction would undo the capture. I'm reading error in your method of assembly.
I understand what you are saying Redfish, but I am cognizant of the correct assembly procedures for removal and assembly of these components so as to not damage these parts by inadvertently prying/forcing them apart when installing them. The capture of the ball joint by the rim should not be finger tight or less. The press fit of the first ball joint to the lower arm actually fell apart before any installation was attempted. It happened while I was holding the lower ball joint in my hand while preparing to fit the rubber shield.
On the replacement lower ball joint, Once I bolted the lower arm to the spindle and then attached this ball joint assembly to the lower control arm, the weight of the spindle, caliper mount and dust shield was enough to pull the ball joint out of the cup. There was no force other than the simple weight of the parts. That should not be able to separate this press fit. If it was, the added weight of wheel and tire during actual use would compromise the attachment.
The assembly needs to capture the ball joint with enough force as to require significant prying apart of the assembly to get them to separate. The ball joint itself should be as strongly attached to the lower forged arm as the upper ball joint is to the upper control arm.
The way these joints are joined together, any unweighting of the front suspension that allows the tire to come off the ground would allow the lower ball joint to fall out of the socket. There are several mountain roads I use on annual trips that find the car catching a bit of air on certain sections. I'm not talking about doing Duke's of Hazard jumps, but I have caught an inch or so of air over rolling roads at speed. These ball joints would have been a recipe for disaster.