Murderous policies usually outweigh one man or figurehead. Did Hitler, Pol Pot and Pinochet hypnotize those willing to kill for them, or did they merely tap into shared grievances and hatreds and exploit them? All had top aides and lieutenants who, had the historical circumstances been the same, would have gone forward with more or less the same programs. But then, this is conjecture, as is your claim that great suffering would have been prevented has they been iced.
Had Hinckley killed Reagan, would the contra policy been killed off as well, sparing tens of thousands of Nicaraguan lives? Probably not, especially since it began with Carter and continued to its logical end under Bush.
DP