Over the years,I've read and heard repeated warnings by various experts
that driving a blank onto a morse tapered spur center while it's on the
lathe will damage the bearings.

Sounds like one for MythBusters. A large axial force, whether by hammer or arbor
press, can and does damage bearings. Ball bearings can carry a large radial
load, but their ability to carry an axial load is a fraction of their radial
load. Hence the warnings. I doubt that the light whack of setting a spindle on a
drive center is going to cause problems in a heavy duty lathe.

I can see that if a spindle is axially free except for being locked onto
the bearings, banging it axially would damage the
bearings. Are the spindles of most of our lathes attached to the
bearings tightly enough to cause damage by axial pressure?

Most commercial lathes' spindles are retained by the front set of bearings
alone; not the rear set, which are often made to float, but occasionally both. l
have never seen a case of the spindle being held in place by anything else
except the bearing(s) such as the pulley. How could it/? The pulley is not fixed
to the headstock. It is the front set that takes all the abuse, hence they are
often larger, double, or roller bearings instead of ball. Mine is an 1.5 inch
bore double angled roller bearing, weighs about five pounds.

Dan