Why do so many idiots write movies?
Unless you have more than 1 hostage, there's no point in having a hostage.
Let's look at this from a logical perspective:
Your ultimate goal in a hostage situation is leaving without going to jail. You're threatening someone that, if you don't get to leave, you're going to kill someone else. But, if you shoot the hostage, you're going to jail.
If the cop shoots the hostage, which does happen, you're going to jail.
If you don't shoot the hostage, you're going to jail.
Hostages are for buying time, not bargaining. Once you're bargaining with hostages, the game is pretty much already over.