U-joint on steering shaft: float or bolt down?

Because the U joint could "float" right off the steering box. The column is collapsible, unlike a driveshaft; and the length could change resulting in the column becoming disconnected from the steering box. There are supposedly plastic "shear pins" in the column to restrict movement, but how many of these are actually intact after all these years?
The pot coupler is actually to allow limited fore and aft movement of the column or box while still allowing flex during rotation of the column. Its this fore and aft movement that the U joint does not account for. Look at the length of the splines on a transmission/slip yoke and compare that to the steering box- nowhere near enough to be safe.