I dont think its anything to do with making the computer hard to use (although that could certainly be a side effect), but the fact that talking to hardware usually means poking at memory, which has security implications and is probably the bigger concern.
As for capturing the image from an optical mouse sensor, I doubt youre going to achieve that with a stock standard mouse. A mouse isnt designed to work as a camera in the traditional sense, so probably doesnt contain the ability to ship its images off to the PC, just information about movements.