Sorry, but that's a particularly irresponsible statement, as what you describe is unsafe gun handling procedure. The safety is disengaged only when the rifle is mounted to shoot. If you've stopped, mounted the rifle and are waiting on the shot, fine, the safety can be off. At any other time, the safety of a rifle or shotgun should be "on". This is especially true when you're under stress and expecting the need for a snap shot any second - because people make mistakes under stress, and that's when failure to follow proper procedures are so potentially fatal. That's why safety procedures are drilled - so that you'll do what you trained under stress.

One of the most important aspects of good safety design is speed of use and, unfortunately, it's also the one most often ignored. With a long gun, if having the safety engaged makes ANY difference in the elapsed time between "Oh shit" and "bang", whether the shooter is expecting a snap shot or not, then there are only have two choices: 1) the shooter hasn't mastered the weapon well enough yet to be using it in the field, or 2) poor design - and this is more true with the double rifle than any other weapon. With a good design, and a competent shooter, there's zero incentive to punch off the safety until the instant the shot is wanted, as doing so offers zero speed advantage, and therefore, no incentive to violate safety procedure. Safety designs become inherently more dangerous as they become more cumbersome, because of the user's tendency to avoid the problem by punching the safety off prematurely. I was very nearly killed when another hunter did exactly what you described for exactly that reason, and have zero tolerance for such nonsense.