A mass storage device is supposed to contain data, and possibly software. When you connect a MSD, in general, you probably want to access the data inside it - its filesystem.

If an "autorun" system is implemented, and on by default, MSDs become a hefty vector for circulating malware - it takes little to foresee it. This happened - and out of a really bad idea: "connecting a device" is in general not to be interpreted as "wanting to run software".

About instead the «normal/actual user» (though I do not understand how it is relevant), well, if said user connected a MSD, a data container, and were prompted that some code "wanted" to be executed, the user is supposed to react in terms of "WTF?!". Exceptional classes of cases can be managed - but really, the advantage of avoiding opening the device filesystem and starting an executable is less than negligible. When such behaviour is desired, a system should be specialized for that whole framework (and should revolve around the design concept of "trusting software").