system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] If the killing curse is unblockable, why are wizard duels a thing at all?

Especially with death eaters involved. Why should they care if a spell is illegal or whatever?
gpt
Even for a totally unscrupulous rogue wizard, the Killing Curse is not an ideal weapon in most duels. It is slow, for one thing, compared to most hexes and charms that an accomplished wizard can cast without even using an incantation. One takes concentration, force of will, and no small amount of unfiltered hatred, and the other is a quick flick of the wrist. Against a ready and capable opponent, you would need to be lucky or supremely powerful to complete the spell.

While it cannot be countered or shielded against using conventional defensive spells, a trained Auror is able to dodge and use cover. This is the type of combat training that isn't learned by the majority of wizards and witches, since protective magic is usually more than sufficient. This makes the Killing Curse a terrifying weapon of fear against the general public, but against a resolute defense dark wizards generally resort to more straightforward tactics to incapacitate their opponents.

Not to mention that the Unforgivable Curses are a high class of magical crime that many low level criminals are reluctant to take on. Robbery and assault earn the offender a stint in Azkaban. The Killing Curse often means the Dementor's Kiss.