I don't know if I think they should have "heavy" pulls, but they shouldn't be light. Most of us civies will go our whole lives never "covering" a person with the muzzle of a loaded gun. LEOs are quite like to have to do so a lot. A peace officer who, in the heat of the moment accidentally pulls the trigger has just, as an officer of the state, executed someone, and likely someone who could not legally have been sentenced to death. If one buys the old addage that it is better to let 10/20/100 guilty men go unpunished than have one innocent man wrongly punished, then even one discharge that the LEO would have foregone with an extra .01 second to consider is unacceptable. I'm very sympathetic to the trauma that LEO's face in having made the split-second decisions about whether to pull that trigger or not... if a stouter trigger saves one cop a year from a shoot that he or she regrets, that's pretty positive.
At some point, of course, the trigger becomes so heavy that the accuracy loss and resultant stray bullets endanger more innocent people than the lighter trigger would have.