After careful consideration, I feel the fumble out of endzone and other team gets the ball at the 20 is the worst rule in not only football, but all professional sports in the entirety of the last century. It makes no sense whatsoever to give the other team the ball when they didn't recovery the fumble. Moving the ball out to the 20 is good but the team fumbling the ball should keep possession, just like when you fumble out of bounds.
Analogies that I can think of that would be comparable.
1) Baseball - Hit a foul ball and the inning is over and the other team gets a runner at 2nd base. Proponents of the rule may say, hit the ball in fair territory and you don't have a problem.
2) Basketball - Dribble the ball out of bounds off your foot and the other team gets to shoot 2 free throws. Proponents of the rule may say, take care of the ball and don't dribble it off your foot.
3) Hockey - Shoot the puck over the net and into the crowd and the other team gets a penalty shot. Proponents of the rule may say, don't shoot the puck out of bounds.
The rule is so dumb in football, that it is a miracle that somebody hasn't figured it out that is in charge yet. Simply, it is the worst rule in profession sports history. Just awful!!!!