Perhaps, but left-foot braking is a useful technique, and common practice in some forms of racing.

In street driving, the main application is being ready to brake while driving normally. It is much faster to brake with the left foot hovering over the brake pedal than by moving the right foot from the throttle to the brake. Of course covering the brake pedal with the right foot precludes driving normally on a flat road or uphill.

This should of course be practiced in low-risk situations before being attempted in high-risk situations.