What you're saying is completely untrue. Electronic equipment is not
designed that way.

Ok, in the case of reverse polarity -will there be any voltage in the
CD player even after it is the CD PLAYER switch is switched off? That
won't have whatsoever effect on diodes and other components?

If the player does not have a "hard" power-supply switch -- and many
don't -- there will be a turn-on circuit that draws a bit of power. But
there would no reason for leaving the main power supplies on -- and
especially (in a device using balanced supplies) leaving one on and the
other off.

No designer in his right mind would leave the laser diode running all the
time. They have a limited lifespan, and you don't waste it.