...and when one unit is having a rough day you want the other unit to step it up and help pick up the other.
It's like back in the Crowton era when he used to take crazy chances on offense which would not work out and then would hang the defense out to dry leaving them with their backs up against the wall in a difficult situation with a short field to defend. I remember reading that there wasn't much harmony between the D and the O back in those days.
The defense's success shouldn't come through stealing opportunity from the offense any more than the offense shouldn't be wreckless and cavalier and hang the D out to dry.