Let's see now. A/P engaged and pilot has hands on knee monitoring the automatics. Something dreadfully critical happens and after the normal one second human response delay, one of the two monitoring pilots grabs the controls. That would take maybe one second.
Scene 2. As above except automatics engaged but PF (or PM, if you so desire) has mitts on controls as well. A dreadful event occurs and after the one second evaluation period the PF tightens his grip on the controls. That takes maybe half a second.
So now we are looking at an emergency that is so deadly that one half of one second is all there is between life or death.
Seems there is no shortage of nervous nellies masquerading as airline pilots.