it's not clipping that damages speakers, but Power.
if you increase the volume to the point where there is heavy clipping, then the amp is in effect putting out more power than it was designed for, and it's this power - if sufficiently high - that will destroy speakers.
if a 50 Watt amp is clipping heavily and the total power going to a speaker is 100 watts and the speaker can take let's say, 125 Watts, then those speakers will be fine, whatever the form of the signal; even if it would be a triangle wave (resembling the teeth of a saw).
the speakers don't know the difference between a clean signal or a distorted one; they only thing they know is "power", and too much of it will heat up and break the speaker.
i would not qualify what you refer to as being "wisdom", but a myth invented by people who imagine an answer for a given unknown or problem, and then "make" it a truth.
it's a bit like the difference between religion and science.
