I think of it like this when it comes to reptiles and what have you...if you have a few generations of reptile born, bred, living in captivity...they wouldn't really know any better. For something that's always been in an enclosure or tank or anything, what they live in is all they know.
I think there's a little voice in everyone's mind that's very very quite in saying "you know this is wrong, why do it?" but to me that's how I've always thought of it. If something (or someone) is born in a certain situation, and pretty much blocked off from something (like being in the wild) then how would it know?
That's just my 2 cents on it