Having a self destruct feature that automatically engages when an airplane is hijacked would also make make hijackings unviable.
If you respond as if the hijackers are suicide bombers, when they really only want a ransom, then you risk some or all of the hostages getting injured or dyeing, as well as the potential for the plane, which would otherwise have landed safely, to crash into a populated area as the hijackers are distracted from piloting the plane, or the passenger may decide to be heroes and take over (crashing either deliberately or by accident).
If you respond as if the hijackers are suicide bombers, when they really only want a ransom, then you risk some or all of the hostages getting injured or dyeing, as well as the potential for the plane, which would otherwise have landed safely, to crash into a populated area as the hijackers are distracted from piloting the plane, or the passenger may decide to be heroes and take over (crashing either deliberately or by accident).