Yes, good point Dejain , he might not have surrendered without taking lives, but that's why the officers  with their advance warning needed to take defensive positions and have a contingency plan.
Had they tased him before there was any sign of a gun being drawn there would have been no need for any shooting.   Had they remained in defensive positions and  waited to fire until they actually saw a gun in his hand he still would have been killed  had he drawn but would not have  gone down as their martyr.  The gun in his dead hand would  have been proof to all but the most obsessed that he needed to be shot, tragically
This is a dangerous movement of hostility to the federal government going on across rural America that's drawing  even good folks in to it, and the last thing we needed was the creation of a powerful new  martyr figure. 

[Question for law enforcement experts: when is it justified to shoot a dangerous suspect before a weapon is actually seen in the suspect's hand?]