Cops knock on the wrong house, a man answers with a gun, and the man ends up dead. I feel fortunate to live in a good neighborhood where SWAT raids are not a regular occurrence, because if someone breaks down my door early in the morning, without announcing their intentions, I’d probably be found in the same position: SWAT team in the living room with me visibly armed. I’d likely suffer the same fate unless I can ascertain they are indeed police officers quickly enough.
I would point out, if it wasn’t for the War on Drugs, we’d have relatively little need for this kind of military tactic. No knock warrants are generally used to prevent destruction of evidence, which if you’re going to do, you had better be sure the crime warrants putting people’s lives at risk. I don’t think preventing people from getting high is worth that, personally.