Downshifting an automatic, Is it bad? Options

[YellowTwo]

Somebody told me that downshifting in an automatic is bad for the transmission because it forces it or something.... I have never heard this and I don't know why the manufacturers would let you do it if it's bad for the car. Any ideas on whether this is fact or fiction?

[Consynx]

an automatic in D at a stop light is like a manual at a stop light(but on verge of letting clutch grip)...so it would seem better to have it in D.
as for breaking, N would stop a forward press, but it's meaningless because when breaking an auto has a safety neutral thing that automatically goes to the same circumstance as at a full stop.

Now, shifting into L is generally retarded unless towing something, like the manual suggests. but a 2nd gear wouldn't see irrational...i mean, if u need to slow down quicker at least, not accelerate.
the tranny would take more of a beating, but the brakes would take less...it's your choice