Gulfstream V crew declines to accept an ATC clearance to descend without an off course deviation due to thunderstorm activity below his aircraft.

Narrative

I was en route and there were two rather large thunderstorms. I was northbound directly between the two at FL450 and above the anvil connecting the cells. Although we were above the storms; the turbulence made it clear that there were much worse conditions directly below us. We received a clearance to descend from FL450 to FL350. I politely declined the clearance and stated that if we had to descend we would have to perform a 180-degree turn to the south in order to avoid the severe weather below us. The Controller responded; 'You have to descend just like everyone else!' To this I replied; 'Negative. We will maintain FL450.' The Controller asked; 'Are you declaring an emergency sir?' I replied; 'No sir.' The Controller indicated that he had reported the 'incident' to his Supervisor. I acknowledged this. He said; 'You can't just deviate from a clearance without declaring an emergency.' I explained that I didn't deviate from a clearance I simply did not accept the clearance he attempted to assign to me. As well; I offered alternate solutions to the problem of needing to descend. Upon being passed over to the next Controller; we were in the clear and able to descend without encountering the severe weather we had just flown over.I make this report to bring attention to the ATC system problem of the over controlling Controller. Controllers need to be aware that the captains of these aircraft have the lives of the people in them in their hands...not the controllers. Had I accepted this clearance and descended into the severe weather someone may have bee injured and it would have been my fault. Just as if a Controller gave me a clearance to take a runway for departure with an aircraft on short final to that same runway; I would not accept a clearance that will bring imminent danger to my aircraft and its occupants.