Well, it seems that you may not understand much of what you are talking about. First off, the 10 or 50 000 V quoted on tasers is the peak unloaded voltage (it's 50 kV for the M26 taser) . With a load like a human body it is more like 5000 V peak (1500 V average). Typically a lethal current is in the 100 mA range (sustained), and that is 100 mA through the heart. The M26 taser has an average current of around 3.6 mA. You've mentioned 500 000 ohms and that is actually close the resistance of dry skin. Also, the power output of a taser is about 7.4 W (the ADVANCED TASER M26 uses 8 AA batteries). Since the device is power limited, higher voltage results in lower current, so higher voltages are safer.