Your argument seems to hinge on the meaning of "impetus." If a blocked punt, which clearly changes the direction and destination of a ball can be considered to not change the "impetus" of the ball, then it is little different that a defensive player stripping an offensive player of the football likewise does not change its "impetus."
It makes little sense for a team who fumbles the ball out of their own end zone to be rewarded a touchback and a "do over" from better field position. Otherwise, this would be a common strategy.
Your opponent downs a punt on your 1 yard line? No problem, just fumble the ball out of bounds on your first play and resume with a new set of downs from your 20.
SD
First, Dallas didn't fumble in their end-zone. The receiver was clearly out of the end-zone. Maybe if he was on his own ten (instead of the one) this would be clearer to everyone. The ball was knocked out of the receiver's hands by a Seattle player. Can you imagine having a safety called if the Dallas guy was on his ten, or twenty?
Second, I never suggested that the touchback rule makes sense. (I don't even like the more usual touchbacks.)
Third, it won't likely become a strategy to fumble at ones own one yard line as there is at least a 50-50 chance any such fumble will be recovered for a TD.
ML/NJ