Not wrong . FWIW , I've been driving autos just as long (must be a 'mile millionaire' in them by now) .
It IS 'wrong' the way most people drive manual cars , going sequentially up and down the gears , the way novices are taught at driving schools , and one of the first things that is drummed out of people as soon as they take advanced lessons .
Just because a lot of people do something , and never progress beyond the novice stage , does not make it 'right' .
God gave most of us two feet , and Mercedes-Benz put two pedals in front of them : it is as illogical to drive an automatic car using only one foot as it would be to hop around on only one foot instead of walking .
Just because a lot of people start out on manual cars , and get 'used' to driving them using the right foot to brake , does not mean that using the same foot to brake in an automatic is 'right' also .
'newbie' automatic drivers would do well to start out using the automatic brake pedal as they would the clutch to control the movement of the car when manoeuvering at low speeds , since the operation is essentially the same : lift the pedal , the car starts to move &vv ; later they can progress to using the left foot when slowing for planned stops . Before long , it WILL become second nature , and a MUCH more efficient way of driving the car .
Reluctance to do this is just the same as many peoples' reluctance to even TRY driving an automatic - there is some irrational fear that cannot be explained .