Right, but the server is still receiving data from the client. If the client sends a plausible head shot, even though it was actually a miss, how would the server know? You still need client-side "police", AKA anti-cheat software to mitigate a significant type of software-based hacks.

Now that I've typed it out, cops are actually a great analogy to anti-cheat software. Cops play the exact same role. Nobody wants them around until a crime has been committed. Cops/anti-cheat software don't catch everyone, but the threat of being caught mitigates some crime/hacks, and for the cases where criminals/hackers are caught, society/gamers are better off for it.

In closing ACAB - I completely understand why we don't want anti-cheat software on our computers, but there really is no better way; or if there is, I still haven't heard it.