The response was correct. If the man was currently posing an immediate threat to police or others, then shoot him or tase him. If not, take him into custody and give him a fair trial. Then lock him up, probably for the rest of his life (or put him to death, I suppose, but I don't think that's a power our justice system should weild).
There will always be corruption and abuse in any institution. You would absolutely not want to live in a society that gave police officers the powers of judge, jury and executioner, in addition to the formidable and potentially dangereous powers they already have.
What this guy did was discusting. Had I seen it I probably would have hit him in the head with a rock and continued hitting him until his head was essentially no longer there. Just because you want to hurt someone doesn't mean that there would be no negative consequences for expanding the powers of your government to act on your personal, volatile emotional impulses.