First of all, you're almost saying whistle for a penalty is the same thing as scoring it. It isn't.
Secondly, all the players knows that inside the area only the keeper can touch the ball with his hands. That is not the same as the ball touches the hands or the arms. So, defenders (or the best of them) always defends with their hands in their backs.
One thing is deliberate touch it, one thing is the ball by the kick's power or a detour touches one's arms or hands. That is not a penalty. Canada is right (i saw it on a Tv's report). The lucky bounce as you say it, is not about luck at all, because it is a fault made by the defender (or any player), not by the ball coming to a defender.
The debate is all about the technology being part of the game. There are a few introductions in the last years, but they are almost secondary (like the ref's headphones). You have to understand significant part of the worldwide success of football derives from the fans' discussions. Football wouldn't be the same if you couldn't discuss the goal of the 1966 World Cup final or Maradona's hand goal in 1986.
The International Board is very conservative to implement major changes in the sport. Because they agree that mistakes, by nature, are part of the game. Players can fail, the managers can fail, so can referees.
Football industry is a relatively recent news to the sport, so it is a difficult balance, if you think about it.