I have been driving since I was younger than you, and I do not left-foot brake, even in an automatic.
This is due to a number of reasons:
1. I will drive anything I am allowed to
2. I have been driving for 40 years and manual gearboxes were the standard when I was your age
3. I believe in automatic reflexes, which means that I do not have to think about whether the car I am driving at the time has two or three pedals in an emergency to decide which foot to brake with.
4. There is NO driving situation where you need to have your foot on both the brake and accelerator (gas) simultaneously - automatics cope best on hill starts, Subaru's "hill holder" works well on manuals, and manual gearboxes require you to have foot on clutch pedal starting uphill, so....
5. If the pedals layout has been properly designed (yeah, I know) the brake and accelerator pedals should be at the same height, so you don't need to lift and move the right foot across, just swivel the ankle.
6. Motor Sport car builders/modifiers adjust the pedals so that all three are in the same plane.
7. you need your foot off the gas when braking in a hurry, as you need all the stopping power under your control - not having to fight the engine.
8. There is nothing worse (well there really is but...) than a driver "riding the brake pedal" because they are so nervous. It is sheer bad driving and makes anticipation by the following car's driver so much more difficult. If the brake lights are constantly on, you can't tell if they are seriously braking until later than you would want - doesn't do your own gut a lot of good.
9. Your reaction time MAY be better with left foot braking - MAY BE. Marginal; but what about the loss of efficiency with the foot still on the go pedal
Rally drivers in front wheel drive cars, used to use left foot braking the get the rear of the car sliding, whilst powering on hard on the gas. Equivalent effect of a "handbrake" or "bootlegger" turn.
Stick with your parents concepts