Connect a 2 wire grounded out let to a 2 wire ungrounded wire cable
In an older system, since both the ground wire and the neutral wire connect to the same point in the breaker box, why can't I install a 2-wire grounded outlet into a box with older NM, 2-wire with no ground wire system, by connecting the outlet safety ground to the neutral wire in the outlet box?
First, because it is against code. Then, even though the neutral and ground connect at the panel, they are not connected in the field. By connecting them in the field, you turn all ground conductors into current carrying conductors, just as the neutral is. It is dangerous.
The reason you don't do as you suggest is this. If the neutral becomes disconnected between the receptacle and the panel now all the grounded parts of your device are live at 120 volts. The current flows into the device on the hot and out the neutral and onto the ground which is connected to any metal surfaces of your device. It has no path back to the panel, so the device will not operate. If you touch the metal frame and something that is a true ground you become the path for current flow.