Of course pesticides and air pollution are not the only causes of premature deaths. But you are wrong about life expectancy in the US. It is behind other first world countries and is on track to drop again in2018 for the third year in a row. The following article references the CDC statistics.
While I agree with your hypothesis about Roundup, I disagree with your premise about life expectancy in North America. According to the CIA factbook and the WHO the America’s are in the upper third world wide when it comes to life expectancy, that despite often truly terrible dietary habits, a diabetes epidemic especially among children and a junk food industry that treats hamburger meat with ammonia.
Diesel, pesticides or Roundup can’t be figured as the sole culprits here.