switch mode power supply = trash?

Probably like everything else, there is no 'definitive' answer. Poorly realized switching power supplies will be 'trash', well-realized ones will sound much better. So, for example, David Berning's amps use switching power supplies, and while some may not like the sound, I daresay no one would call the amps 'trash'.
BTW, I assume we're talking about the same thing, my 'switching power supply' is your 'switch mode power supply'.

In the world of audiophiles there is no such thing as a "definitive answer". IMHO, it all depends on how the power supply, of either kind, is designed. Either one produces DC power, with little noise riding on it. The switching power supply has many practical advantages, perhaps the most useful being ability to operate using a wide range of AC power input (no need for step-up or step-down transformers to sell in the global marketplace). The switching power supply can react more quickly to transient demands. Its output noise is at a high frequency, which is easier to filter out than the 120 Hz ripple from a conventional power supply, but some folk think that HF noise (which they like to call RFI) has an adverse effect on their electronics.

Is there someone who is a linear power supply adept, who can explain (in an accessible fashion) why with regard to audio linear power supply is superior to SPMS?

Chris