The only reason it feels more natural to you is because that is the way you do it. It was beat into me from Driver's Education never use your left foot to brake. To me it feels natural to not brake with my left foot.
There is a great article I just read about using your left foot to brake from a driving instructor. In the article he basically says things I was thinking. There are a couple of points he makes in the article I want to point out. This is directly related to when he was instructing his students to use their right foot to brake.
We do emergency braking in a controlled environment at Young Drivers of Canada so I had the student apply the brakes with their left foot when I suddenly commanded “STOP!” at a specific speed and location. I measured their stopping distance and then had them try it again with their right foot applying the brakes. Their stopping distance was hugely improved. I never had to remind them again about only using their right foot on the pedals.
While this is doesn't have very much empirical data in it, it rings true for the following reason (as he goes on to say):
The main difference for an improved stopping distance was their left foot was able to counter balance their weight transfer so they had more pressure to apply into their braking. If your left foot is placed up against the firewall of the vehicle, it can allow you to push yourself back in your seat. That will then allow you to press harder against the brake pedal in an emergency. Sit in your vehicle while parked and try this. You will automatically feel the difference in leg strength when you apply the brake this way.
Another thing you probably don't think about is a lot of people who use their left foot to brake actually keep their foot on the brake pedal. If you do this and think you are not causing issues, you are sadly mistaken. When you keep your foot on the pedal, you are riding the brake. This does the following:
- Wears out your brakes faster
- Causes you to have worse gas mileage
- Causes undue wear and tear on your drivetrain
Even if you don't believe you're putting any pressure on the pedal by resting it there, you are utterly wrong. The reason I know you are wrong is because not a person in the world is going to be able to keep their foot in the air (off the floor) for any long length of time without fatigue. When fatigue sets in, you rest your foot on the pedal. I have fairly long feet and know I could not rest my foot on the floor and have it in a position to brake at the same time.