This is one of those circular debates without end so I'll say my last piece.
I can fly an aircraft just above the stall and, as long as no 'upset' occurs, all will be well.
So, by the same token, I can fly an airbus below the manufacturer's manoeuvre speed (which they also refer to as the 'target' speed for that configuration) and all will be well.
However, are either of the above examples of good airmanship............I don't think so!
Vls is a protection that exists when the A'Thr is engaged.........nothing else.
Manoeuver speeds are designed to give a margin of safety for manoeuvre in certain configs (hence the boeing -20 kts thing.............that's the margin).
Flying below that speed reduces the margin and negates the point of it being there in the first place.