Hi Sandra,
I don't think you're beating anything to death - but I trust that most
of your remaining questions about fencing etc. for multi purpose dogs
were answered by Randi and Jan.  I will however try to answer your
specific questions to me ...

"Are you saying then, that you would not be comfortable with using a
dual purpose dog unless you had dogproof fencing?"

I don't own a dual purpose dog, so can only answer this as it relats to
BCs - so the answer is yes.  However no fence is truly dog proof. As you
and others have pointed out, a dog can always climb out or dig under or
the neighbor kid could open your gate,etc. The fence however IN MY STATE
would probably give me some protection against having to pay incredably
high damages costs if the worst happened.

"Realistically is this possible since it would mean fencing most of the

My entire farm is fenced and crossfenced (including the yard) and there
are gates on the driveway.

No confinement method is a sure bet and if boundary training is your
best option, then it's a good one.  Certainly better than not training.
"How can so many people keep them as pets?"
Border Collies DO come from various lines that are decidedly
specialized, show, obedience and working (herding). Most owner and
breeders of dogs from strong herding lines agree that they do not make
very desirable pets however those from show and obedience lines
frequently do.
Many of the latter also show no desire to herd. But not necessarily.

Since you wanted a multi purpose dog you probably made the right choice.