Seriously? Do you think: 1) Terrorists don't recognize the value in kidnapping our soldiers/Americans? 2) That the only thing preventing them from doing so is their own desire?
If they could kidnap our soldiers, they would kidnap our soldiers. They just can't. So they don't.
But for a moment, if you believe this nonsense, consider this: If in fact negotiating for Bowe Bergdahl's release did increase a terrorist's desire to kidnap our soldiers, isn't it quite possible then this would stop a terrorist from killing them?