I would bet that the sort of people who think it's horrific that cops would shoot people wielding knives also tend to be the sort of people who loathe Tasers.
That's right. If the bad guys come at you with an inferior weapon you are obligated to:
*Retreat so they or you don't get hurt.
*Drop your superior weapon and pick up one like theirs to make it fair.
*Drop all weapons entirely and beg for mercy.
After some reflection, I've actually re-considered the UC Davis action that resulted in pepper spraying the seated and arms-linked demonstrators. It was still an inferior method that a hit with a taser might have unlinked all or most them in one fell swoop. Certainly better than the spasm and hunch over in a fetal position the pepper spray accomplished.
There's nothing trigger happy about shooting a guy charging at you with a machete. The Mythbusters found that a person with a knife can kill someone with a gun before they get shot as long as they're within 21 feet. Or something.
When cops tested this, they found it was about two feet more, and with a machete it would be about another foot.
Cops are easy targets to criticize, find any other number of cases of cops being dumbasses.