It's so important that Darlin thought they were doing the right thing by keeping distance from the Pack while on the hunt for Quinn.
They thought if they didn't have anyone left they were close with, Quinn wouldn't have anyone he could leverage to hurt them again. They thought he would have to attack them directly. And they could take him. They knew it, Quinn knew it. They were physically strong enough to fight him, to hurt him, maybe even kill him if they died trying in the process. But they had a good heart, a soft heart. They cared about innocents. And Quinn used that against them before.
They didn't want that happening again. They cared too much about the Pack to put them in that kind of direct line of fire that only they could handle.
But that's where David saw the failing was. That's where the thought of protection wasn't enough for him. Because Darlin still cared. And Quinn would have been able to tell. Quinn would have lured any one of the elders, the youngsters, Angel or Baaabe into an impossible situation for the whole Pack. An irreparable situation.
As it was, Darlin did get close enough to someone again that Quinn could use against them. Sam. And it cut them deeper than physically attacking the Pack.