That is the central message of the new and excellent Kill Anything That Moves: The Real American War in Vietnam, by Nick Turse.

For the entire course of the war, Turse considers an estimate of 2 million civilian Vietnamese dead and 5.3 million civilian wounded. Of course by no means were all of those the result of U.S. military action but many were. Here is a staggering estimate:

…between 1965 and 1968, thirty-two tons of bombs per hour were dropped on the North.

And yet, in fact, even more tonnage was dropped on the South, the ostensible ally! The total quantity of explosives dropped is estimated to have been equal to 640 Hiroshima-sized atomic bombs.

There is a very good review of this book here.